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The comment about unregistering boot consoles is just not matching the
reality. Remove it.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220924000454.3319186-5-john.ogness@linutronix.de
Commit a699449bb1 ("printk: refactor and rework printing logic")
removed the need for @nr_ext_console_drivers. Remove the unneeded
variable.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220924000454.3319186-4-john.ogness@linutronix.de
No user outside the printk code and no reason to export this.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220924000454.3319186-2-john.ogness@linutronix.de
The console_stop() and console_start() functions call pr_flush().
When suspending, these functions are called by the serial subsystem
while the serial port is suspended. In this scenario, if there are
any pending messages, a call to pr_flush() will always result in a
timeout because the serial port cannot make forward progress. This
causes longer suspend and resume times.
Add a check in pr_flush() so that it will immediately timeout if
the consoles are suspended.
Fixes: 3b604ca812 ("printk: add pr_flush()")
Reported-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Tested-by: Todd Brandt <todd.e.brandt@linux.intel.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220715061042.373640-2-john.ogness@linutronix.de
This reverts commit 2bb2b7b57f.
The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.
It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.
printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.
Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-7-pmladek@suse.com
This reverts commit 09c5ba0aa2.
This reverts commit b87f02307d.
The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.
It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.
printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.
Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-6-pmladek@suse.com
This reverts commit 8e27473211.
The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.
It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.
printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.
Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-5-pmladek@suse.com
This reverts commit ab406816fc.
The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.
It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.
printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.
Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-4-pmladek@suse.com
This reverts commit c3230283e2.
The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.
It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.
printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.
Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-3-pmladek@suse.com
This reverts commit b87f02307d.
The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.
It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.
printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.
Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-2-pmladek@suse.com
There are reports that the console kthreads block the global console
lock when the system is going down, for example, reboot, panic.
First part of the solution was to block kthreads in these problematic
system states so they stopped handling newly added messages.
Second part of the solution is to wait when for the kthreads when
they are actively printing. It solves the problem when a message
was printed before the system entered the problematic state and
the kthreads managed to step in.
A busy waiting has to be used because panic() can be called in any
context and in an unknown state of the scheduler.
There must be a timeout because the kthread might get stuck or sleeping
and never release the lock. The timeout 10s is an arbitrary value
inspired by the softlockup timeout.
Link: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1
Link: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20220615162805.27962-3-pmladek@suse.com
There are known situations when the console kthreads are not
reliable or does not work in principle, for example, early boot,
panic, shutdown.
For these situations there is the direct (legacy) mode when printk() tries
to get console_lock() and flush the messages directly. It works very well
during the early boot when the console kthreads are not available at all.
It gets more complicated in the other situations when console kthreads
might be actively printing and block console_trylock() in printk().
The same problem is in the legacy code as well. Any console_lock()
owner could block console_trylock() in printk(). It is solved by
a trick that the current console_lock() owner is responsible for
printing all pending messages. It is actually the reason why there
is the risk of softlockups and why the console kthreads were
introduced.
The console kthreads use the same approach. They are responsible
for printing the messages by definition. So that they handle
the messages anytime when they are awake and see new ones.
The global console_lock is available when there is nothing
to do.
It should work well when the problematic context is correctly
detected and printk() switches to the direct mode. But it seems
that it is not enough in practice. There are reports that
the messages are not printed during panic() or shutdown()
even though printk() tries to use the direct mode here.
The problem seems to be that console kthreads become active in these
situation as well. They steel the job before other CPUs are stopped.
Then they are stopped in the middle of the job and block the global
console_lock.
First part of the solution is to block console kthreads when
the system is in a problematic state and requires the direct
printk() mode.
Link: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1
Link: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com
Suggested-by: John Ogness <john.ogness@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220615162805.27962-2-pmladek@suse.com
This reverts commit 938ba4084a.
The wait queue @log_wait never has exclusive waiters, so there
is no need to use wake_up_interruptible_all(). Using
wake_up_interruptible() was the correct function to wake all
waiters.
Since there are no exclusive waiters, erroneously changing
wake_up_interruptible() to wake_up_interruptible_all() did not
result in any behavior change. However, using
wake_up_interruptible_all() on a wait queue without exclusive
waiters is fundamentally wrong.
Go back to using wake_up_interruptible() to wake all waiters.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220526203056.81123-1-john.ogness@linutronix.de
The original intent of the 'console' tracepoint per the commit 9510035849
("printk/tracing: Add console output tracing") had been to "[...] record
any printk messages into the trace, regardless of the current console
loglevel. This can help correlate (existing) printk debugging with other
tracing."
Petr points out [1] that calling trace_console_rcuidle() in
call_console_driver() had been the wrong thing for a while, because
"printk() always used console_trylock() and the message was flushed to
the console only when the trylock succeeded. And it was always deferred
in NMI or when printed via printk_deferred()."
With the commit 09c5ba0aa2 ("printk: add kthread console printers"),
things only got worse, and calls to call_console_driver() no longer
happen with typical printk() calls but always appear deferred [2].
As such, the tracepoint can no longer serve its purpose to clearly
correlate printk() calls and other tracing, as well as breaks usecases
that expect every printk() call to result in a callback of the console
tracepoint. Notably, the KFENCE and KCSAN test suites, which want to
capture console output and assume a printk() immediately gives us a
callback to the console tracepoint.
Fix the console tracepoint by moving it into printk_sprint() [3].
One notable difference is that by moving tracing into printk_sprint(),
the 'text' will no longer include the "header" (loglevel and timestamp),
but only the raw message. Arguably this is less of a problem now that
the console tracepoint happens on the printk() call and isn't delayed.
Link: https://lore.kernel.org/all/Ym+WqKStCg%2FEHfh3@alley/ [1]
Link: https://lore.kernel.org/all/CA+G9fYu2kS0wR4WqMRsj2rePKV9XLgOU1PiXnMvpT+Z=c2ucHA@mail.gmail.com/ [2]
Link: https://lore.kernel.org/all/87fslup9dx.fsf@jogness.linutronix.de/ [3]
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Marco Elver <elver@google.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: John Ogness <john.ogness@linutronix.de>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220503073844.4148944-1-elver@google.com
The static global variable @console_locked is used to help debug
VT code to make sure that certain code paths are running with
the console_lock held. However, this information is also available
with the static global variable @console_kthreads_blocked (for
locking via console_lock()), and the static global variable
@console_kthreads_active (for locking via console_trylock()).
Remove @console_locked and update is_console_locked() to use the
alternative variables.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-16-john.ogness@linutronix.de
Currently threaded console printers synchronize against each
other using console_lock(). However, different console drivers
are unrelated and do not require any synchronization between
each other. Removing the synchronization between the threaded
console printers will allow each console to print at its own
speed.
But the threaded consoles printers do still need to synchronize
against console_lock() callers. Introduce a per-console mutex
and a new console boolean field @blocked to provide this
synchronization.
console_lock() is modified so that it must acquire the mutex
of each console in order to set the @blocked field. Console
printing threads will acquire their mutex while printing a
record. If @blocked was set, the thread will go back to sleep
instead of printing.
The reason for the @blocked boolean field is so that
console_lock() callers do not need to acquire multiple console
mutexes simultaneously, which would introduce unnecessary
complexity due to nested mutex locking. Also, a new field
was chosen instead of adding a new @flags value so that the
blocked status could be checked without concern of reading
inconsistent values due to @flags updates from other contexts.
Threaded console printers also need to synchronize against
console_trylock() callers. Since console_trylock() may be
called from any context, the per-console mutex cannot be used
for this synchronization. (mutex_trylock() cannot be called
from atomic contexts.) Introduce a global atomic counter to
identify if any threaded printers are active. The threaded
printers will also check the atomic counter to identify if the
console has been locked by another task via console_trylock().
Note that @console_sem is still used to provide synchronization
between console_lock() and console_trylock() callers.
A locking overview for console_lock(), console_trylock(), and the
threaded printers is as follows (pseudo code):
console_lock()
{
down(&console_sem);
for_each_console(con) {
mutex_lock(&con->lock);
con->blocked = true;
mutex_unlock(&con->lock);
}
/* console_lock acquired */
}
console_trylock()
{
if (down_trylock(&console_sem) == 0) {
if (atomic_cmpxchg(&console_kthreads_active, 0, -1) == 0) {
/* console_lock acquired */
}
}
}
threaded_printer()
{
mutex_lock(&con->lock);
if (!con->blocked) {
/* console_lock() callers blocked */
if (atomic_inc_unless_negative(&console_kthreads_active)) {
/* console_trylock() callers blocked */
con->write();
atomic_dec(&console_lock_count);
}
}
mutex_unlock(&con->lock);
}
The console owner and waiter logic now only applies between contexts
that have taken the console_lock via console_trylock(). Threaded
printers never take the console_lock, so they do not have a
console_lock to handover. Tasks that have used console_lock() will
block the threaded printers using a mutex and if the console_lock
is handed over to an atomic context, it would be unable to unblock
the threaded printers. However, the console_trylock() case is
really the only scenario that is interesting for handovers anyway.
@panic_console_dropped must change to atomic_t since it is no longer
protected exclusively by the console_lock.
Since threaded printers remain asleep if they see that the console
is locked, they now must be explicitly woken in __console_unlock().
This means wake_up_klogd() calls following a console_unlock() are
no longer necessary and are removed.
Also note that threaded printers no longer need to check
@console_suspended. The check for the @blocked field implicitly
covers the suspended console case.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/878rrs6ft7.fsf@jogness.linutronix.de
Create a kthread for each console to perform console printing. During
normal operation (@system_state == SYSTEM_RUNNING), the kthread
printers are responsible for all printing on their respective
consoles.
During non-normal operation, console printing is done as it has been:
within the context of the printk caller or within irqwork triggered
by the printk caller, referred to as direct printing.
Since threaded console printers are responsible for all printing
during normal operation, this also includes messages generated via
deferred printk calls. If direct printing is in effect during a
deferred printk call, the queued irqwork will perform the direct
printing. To make it clear that this is the only time that the
irqwork will perform direct printing, rename the flag
PRINTK_PENDING_OUTPUT to PRINTK_PENDING_DIRECT_OUTPUT.
Threaded console printers synchronize against each other and against
console lockers by taking the console lock for each message that is
printed.
Note that the kthread printers do not care about direct printing.
They will always try to print if new records are available. They can
be blocked by direct printing, but will be woken again once direct
printing is finished.
Console unregistration is a bit tricky because the associated
kthread printer cannot be stopped while the console lock is held.
A policy is implemented that states: whichever task clears
con->thread (under the console lock) is responsible for stopping
the kthread. unregister_console() will clear con->thread while
the console lock is held and then stop the kthread after releasing
the console lock.
For consoles that have implemented the exit() callback, the kthread
is stopped before exit() is called.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-14-john.ogness@linutronix.de
Once kthread printing is available, console printing will no longer
occur in the context of the printk caller. However, there are some
special contexts where it is desirable for the printk caller to
directly print out kernel messages. Using pr_flush() to wait for
threaded printers is only possible if the caller is in a sleepable
context and the kthreads are active. That is not always the case.
Introduce printk_prefer_direct_enter() and printk_prefer_direct_exit()
functions to explicitly (and globally) activate/deactivate preferred
direct console printing. The term "direct console printing" refers to
printing to all enabled consoles from the context of the printk
caller. The term "prefer" is used because this type of printing is
only best effort. If the console is currently locked or other
printers are already actively printing, the printk caller will need
to rely on the other contexts to handle the printing.
This preferred direct printing is how all printing has been handled
until now (unless it was explicitly deferred).
When kthread printing is introduced, there may be some unanticipated
problems due to kthreads being unable to flush important messages.
In order to minimize such risks, preferred direct printing is
activated for the primary important messages when the system
experiences general types of major errors. These are:
- emergency reboot/shutdown
- cpu and rcu stalls
- hard and soft lockups
- hung tasks
- warn
- sysrq
Note that since kthread printing does not yet exist, no behavior
changes result from this commit. This is only implementing the
counter and marking the various places where preferred direct
printing is active.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org> # for RCU
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-13-john.ogness@linutronix.de
Provide a might-sleep function to allow waiting for console printers
to catch up to the latest logged message.
Use pr_flush() whenever it is desirable to get buffered messages
printed before continuing: suspend_console(), resume_console(),
console_stop(), console_start(), console_unblank().
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-12-john.ogness@linutronix.de
Extended consoles print extended messages and do not print messages about
dropped records.
Non-extended consoles print "normal" messages as well as extra messages
about dropped records.
Currently the buffers for these various message types are defined within
the functions that might use them and their usage is based upon the
CON_EXTENDED flag. This will be a problem when moving to kthread printers
because each printer must be able to provide its own buffers.
Move all the message buffer definitions outside of
console_emit_next_record(). The caller knows if extended or dropped
messages should be printed and can specify the appropriate buffers to
use. The console_emit_next_record() and call_console_driver() functions
can know what to print based on whether specified buffers are non-NULL.
With this change, buffer definition/allocation/specification is separated
from the code that does the various types of string printing.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-11-john.ogness@linutronix.de
Refactor/rework printing logic in order to prepare for moving to
threaded console printing.
- Move @console_seq into struct console so that the current
"position" of each console can be tracked individually.
- Move @console_dropped into struct console so that the current drop
count of each console can be tracked individually.
- Modify printing logic so that each console independently loads,
prepares, and prints its next record.
- Remove exclusive_console logic. Since console positions are
handled independently, replaying past records occurs naturally.
- Update the comments explaining why preemption is disabled while
printing from printk() context.
With these changes, there is a change in behavior: the console
replaying the log (formerly exclusive console) will no longer block
other consoles. New messages appear on the other consoles while the
newly added console is still replaying.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-10-john.ogness@linutronix.de
It is useful to generate log messages that include details about
the related console. Rather than duplicate the code to assemble
the details, put that code into a macro con_printk().
Once console printers become threaded, this macro will find more
users.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-9-john.ogness@linutronix.de
boot_delay_msec() is always called immediately before printk_delay()
so just call it from within printk_delay().
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-8-john.ogness@linutronix.de
Currently the local CPU timestamp and caller_id for the record are
collected while migration is enabled. Since this information is
CPU-specific, it should be collected with migration disabled.
Migration is disabled immediately after collecting this information
anyway, so just move the information collection to after the
migration disabling.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-7-john.ogness@linutronix.de
When printk() is called from safe or NMI contexts, it will directly
store the record (vprintk_store()) and then defer the console output.
However, defer_console_output() only causes console printing and does
not wake any waiters of new records.
Wake waiters from defer_console_output() so that they also are aware
of the new records from safe and NMI contexts.
Fixes: 03fc7f9c99 ("printk/nmi: Prevent deadlock when accessing the main log buffer in NMI")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-6-john.ogness@linutronix.de
There can be multiple tasks waiting for new records. They should
all be woken. Use wake_up_interruptible_all() instead of
wake_up_interruptible().
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-5-john.ogness@linutronix.de
It is important that any new records are visible to preparing
waiters before the waker checks if the wait queue is empty.
Otherwise it is possible that:
- there are new records available
- the waker sees an empty wait queue and does not wake
- the preparing waiter sees no new records and begins to wait
This is exactly the problem that the function description of
waitqueue_active() warns about.
Use wq_has_sleeper() instead of waitqueue_active() because it
includes the necessary full memory barrier.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-4-john.ogness@linutronix.de
Since the printk cpulock is CPU-reentrant and since it is used
in all contexts, its usage must be carefully considered and
most likely will require programming locklessly. To avoid
mistaking the printk cpulock as a typical lock, rename it to
cpu_sync. The main functions then become:
printk_cpu_sync_get_irqsave(flags);
printk_cpu_sync_put_irqrestore(flags);
Add extra notes of caution in the function description to help
developers understand the requirements for correct usage.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-2-john.ogness@linutronix.de
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Merge tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk updates from Petr Mladek:
- Make %pK behave the same as %p for kptr_restrict == 0 also with
no_hash_pointers parameter
- Ignore the default console in the device tree also when console=null
or console="" is used on the command line
- Document console=null and console="" behavior
- Prevent a deadlock and a livelock caused by console_lock in panic()
- Make console_lock available for panicking CPU
- Fast query for the next to-be-used sequence number
- Use the expected return values in printk.devkmsg __setup handler
- Use the correct atomic operations in wake_up_klogd() irq_work handler
- Avoid possible unaligned access when handling %4cc printing format
* tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
printk: fix return value of printk.devkmsg __setup handler
vsprintf: Fix %pK with kptr_restrict == 0
printk: make suppress_panic_printk static
printk: Set console_set_on_cmdline=1 when __add_preferred_console() is called with user_specified == true
Docs: printk: add 'console=null|""' to admin/kernel-parameters
printk: use atomic updates for klogd work
printk: Drop console_sem during panic
printk: Avoid livelock with heavy printk during panic
printk: disable optimistic spin during panic
printk: Add panic_in_progress helper
vsprintf: Move space out of string literals in fourcc_string()
vsprintf: Fix potential unaligned access
printk: ringbuffer: Improve prb_next_seq() performance
If an invalid option value is used with "printk.devkmsg=<value>",
it is silently ignored.
If a valid option value is used, it is honored but the wrong return
value (0) is used, indicating that the command line option had an
error and was not handled. This string is not added to init's
environment strings due to init/main.c::unknown_bootoption()
checking for a '.' in the boot option string and then considering
that string to be an "Unused module parameter".
Print a warning message if a bad option string is used.
Always return 1 from the __setup handler to indicate that the command
line option has been handled.
Fixes: 750afe7bab ("printk: add kernel parameter to control writes to /dev/kmsg")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Igor Zhbanov <i.zhbanov@omprussia.ru>
Link: lore.kernel.org/r/64644a2f-4a20-bab3-1e15-3b2cdd0defe3@omprussia.ru
Cc: Borislav Petkov <bp@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: John Ogness <john.ogness@linutronix.de>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220228220556.23484-1-rdunlap@infradead.org
This symbol is not used outside of printk.c, so marks it static.
Fix the following sparse warning:
kernel/printk/printk.c💯19: warning: symbol 'suppress_panic_printk'
was not declared. Should it be static?
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220216031957.9761-1-jiapeng.chong@linux.alibaba.com
In case of using console="" or console=null
set console_set_on_cmdline=1 to disable "stdout-path" node from DT.
We basically need to set it every time when __add_preferred_console()
is called with parameter 'user_specified' set.
Therefore we can move setting it into a helper function that is
called from __add_preferred_console().
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andre Kalb <andre.kalb@sma.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/YgzU4ho8l6XapyG2@pc6682
The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:
get_random_bytes()
warn_unseeded_randomness()
printk_deferred()
defer_console_output()
and can be updated from interrupt contexts, such as:
handle_irq_event_percpu()
__irq_wake_thread()
wake_up_process()
try_to_wake_up()
select_task_rq()
select_fallback_rq()
printk_deferred()
defer_console_output()
and can be updated from NMI contexts, such as:
vprintk()
if (in_nmi()) defer_console_output()
Therefore the atomic variant of the updating functions must be used.
Replace __this_cpu_xchg() with this_cpu_xchg().
Replace __this_cpu_or() with this_cpu_or().
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87iltld4ue.fsf@jogness.linutronix.de
If another CPU is in panic, we are about to be halted. Try to gracefully
abandon the console_sem, leaving it free for the panic CPU to grab.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-5-stephen.s.brennan@oracle.com
During panic(), if another CPU is writing heavily the kernel log (e.g.
via /dev/kmsg), then the panic CPU may livelock writing out its messages
to the console. Note when too many messages are dropped during panic and
suppress further printk, except from the panic CPU. This could result in
some important messages being dropped. However, messages are already
being dropped, so this approach at least prevents a livelock.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-4-stephen.s.brennan@oracle.com
A CPU executing with console lock spinning enabled might be halted
during a panic. Before the panicking CPU calls console_flush_on_panic(),
it may call console_trylock(), which attempts to optimistically spin,
deadlocking the panic CPU:
CPU 0 (panic CPU) CPU 1
----------------- ------
printk() {
vprintk_func() {
vprintk_default() {
vprintk_emit() {
console_unlock() {
console_lock_spinning_enable();
... printing to console ...
panic() {
crash_smp_send_stop() {
NMI -------------------> HALT
}
atomic_notifier_call_chain() {
printk() {
...
console_trylock_spinnning() {
// optimistic spin infinitely
This hang during panic can be induced when a kdump kernel is loaded, and
crash_kexec_post_notifiers=1 is present on the kernel command line. The
following script which concurrently writes to /dev/kmsg, and triggers a
panic, can result in this hang:
#!/bin/bash
date
# 991 chars (based on log buffer size):
chars="$(printf 'a%.0s' {1..991})"
while :; do
echo $chars > /dev/kmsg
done &
echo c > /proc/sysrq-trigger &
date
exit
To avoid this deadlock, ensure that console_trylock_spinning() does not
allow spinning once a panic has begun.
Fixes: dbdda842fe ("printk: Add console owner and waiter logic to load balance console writes")
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-3-stephen.s.brennan@oracle.com
This will be used help avoid deadlocks during panics. Although it would
be better to include this in linux/panic.h, it would require that header
to include linux/atomic.h as well. On some architectures, this results
in a circular dependency as well. So instead add the helper directly to
printk.c.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220202171821.179394-2-stephen.s.brennan@oracle.com
The move of proc_dointvec_minmax_sysadmin() from kernel/sysctl.c to
kernel/printk/sysctl.c introduced an incorrect __user attribute to the
buffer argument. I spotted this change in [1] as well as the kernel
test robot. Revert this change to please sparse:
kernel/printk/sysctl.c:20:51: warning: incorrect type in argument 3 (different address spaces)
kernel/printk/sysctl.c:20:51: expected void *
kernel/printk/sysctl.c:20:51: got void [noderef] __user *buffer
Fixes: faaa357a55 ("printk: move printk sysctl to printk/sysctl.c")
Link: https://lore.kernel.org/r/20220104155024.48023-2-mic@digikod.net [1]
Reported-by: kernel test robot <lkp@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
Link: https://lore.kernel.org/r/20220203145029.272640-1-mic@digikod.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
prb_next_seq() always iterates from the first known sequence number.
In the worst case, it might loop 8k times for 256kB buffer,
15k times for 512kB buffer, and 64k times for 2MB buffer.
It was reported that polling and reading using syslog interface
might occupy 50% of CPU.
Speedup the search by storing @id of the last finalized descriptor.
The loop is still needed because the @id is stored and read in the best
effort way. An atomic variable is used to keep the @id consistent.
But the stores and reads are not serialized against each other.
The descriptor could get reused in the meantime. The related sequence
number will be used only when it is still valid.
An invalid value should be read _only_ when there is a flood of messages
and the ringbuffer is rapidly reused. The performance is the least
problem in this case.
Reported-by: Chunlei Wang <chunlei.wang@mediatek.com>
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/1642770388-17327-1-git-send-email-quic_mojha@quicinc.com
Link: https://lore.kernel.org/lkml/YXlddJxLh77DKfIO@alley/T/#m43062e8b2a17f8dbc8c6ccdb8851fb0dbaabbb14
build warning when CONFIG_PRINTK=n
kernel/printk/printk.c:175:5: warning: no previous prototype for
'devkmsg_sysctl_set_loglvl' [-Wmissing-prototypes]
devkmsg_sysctl_set_loglvl() is only used in sysctl.c when
CONFIG_PRINTK=y, but it participates in the build when CONFIG_PRINTK=n.
So add compile dependency CONFIG_PRINTK=y && CONFIG_SYSCTL=y to fix the
build warning.
Link: https://lkml.kernel.org/r/20211129211943.640266-5-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
Cc: Stephen Kitt <steve@sk2.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/sysctl.c is a kitchen sink where everyone leaves their dirty
dishes, this makes it very difficult to maintain.
To help with this maintenance let's start by moving sysctls to places
where they actually belong. The proc sysctl maintainers do not want to
know what sysctl knobs you wish to add for your own piece of code, we
just care about the core logic.
So move printk sysctl from kernel/sysctl.c to kernel/printk/sysctl.c.
Use register_sysctl() to register the sysctl interface.
[mcgrof@kernel.org: fixed compile issues when PRINTK is not set, commit log update]
Link: https://lkml.kernel.org/r/20211124231435.1445213-6-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: James E.J. Bottomley <jejb@linux.ibm.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Julia Lawall <julia.lawall@inria.fr>
Cc: Kees Cook <keescook@chromium.org>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Phillip Potter <phil@philpotter.co.uk>
Cc: Qing Wang <wangqing@vivo.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Sebastian Reichel <sre@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Stephen Kitt <steve@sk2.org>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The variable @bcon has two meanings. It is used several times for iterating
the list of registered consoles. In the meantime, it holds the information
whether a boot console is first in @console_drivers list.
The information about the 1st console driver used to be important for
the decision whether to install the new console by default or not.
It allowed to re-evaluate the variable @need_default_console when
a real console with tty binding has been unregistered in the meantime.
The decision about the default console is not longer affected by @bcon
variable. The current code checks whether the first driver is real
and has tty binding directly.
The information about the first console is still used for two more
decisions:
1. It prevents duplicate output on non-boot consoles with
CON_CONSDEV flag set.
2. Early/boot consoles are unregistered when a real console with
CON_CONSDEV is registered and @keep_bootcon is not set.
The behavior in the real life is far from obvious. @bcon is set according
to the first console @console_drivers list. But the first position in
the list is special:
1. Consoles with CON_CONSDEV flag are put at the beginning of
the list. It is either the preferred console or any console
with tty binding registered by default.
2. Another console might become the first in the list when
the first console in the list is unregistered. It might
happen either explicitly or automatically when boot
consoles are unregistered.
There is one more important rule:
+ Boot consoles can't be registered when any real console
is already registered.
It is a puzzle. The main complication is the dependency on the first
position is the list and the complicated rules around it.
Let's try to make it easier:
1. Add variable @bootcon_enabled and set it by iterating all registered
consoles. The variable has obvious meaning and more predictable
behavior. Any speed optimization and other tricks are not worth it.
2. Use a generic name for the variable that is used to iterate
the list on registered console drivers.
Behavior change:
No, maybe surprisingly, there is _no_ behavior change!
Let's provide the proof by contradiction. Both operations, duplicate
output prevention and boot consoles removal, are done only when
the newly added console has CON_CONSDEV flag set. The behavior
would change when the new @bootcon_enabled has different value
than the original @bcon.
By other words, the behavior would change when the following conditions
are true:
+ a console with CON_CONSDEV flag is added
+ a real (non-boot) console is the first in the list
+ a boot console is later in the list
Now, a real console might be first in the list only when:
+ It was the first registered console. In this case, there can't be
any boot console because any later ones were rejected.
+ It was put at the first position because it had CON_CONSDEV flag
set. It was either the preferred console or it was a console with
tty binding registered by default. We are interested only in
a real consoles here. And real console with tty binding fulfills
conditions of the default console.
Now, there is always only one console that is either preferred
or fulfills conditions of the default console. It can't be already
in the list and being registered at the same time.
As a result, the above three conditions could newer be "true" at
the same time. Therefore the behavior can't change.
Final dilemma:
OK, the new code has the same behavior. But is the change in the right
direction? What if the handling of @console_drivers is updated in
the future?
OK, let's look at it from another angle:
1. The ordering of @console_drivers list is important only in
console_device() function. The first console driver with tty
binding gets associated with /dev/console.
2. CON_CONSDEV flag is shown in /proc/consoles. And it should be set
for the driver that is returned by console_device().
3. A boot console is removed and the duplicated output is prevented
when the real console with CON_CONSDEV flag is registered.
Now, in the ideal world:
+ The driver associated with /dev/console should be either a console
preferred via the command line, device tree, or SPCR. Or it should
be the first real console with tty binding registered by default.
+ The code should match the related boot and real console drivers.
It should unregister only the obsolete boot driver. And the duplicated
output should be prevented only on the related real driver.
It is clear that it is not guaranteed by the current code. Instead,
the current code looks like a maze of heuristics that try to achieve
the above.
It is result of adding several features over last few decades. For example,
a possibility to register more consoles, unregister consoles, boot
consoles, consoles without tty binding, device tree, SPCR, braille
consoles.
Anyway, there is no reason why the decision, about removing boot consoles
and preventing duplicated output, should depend on the first console
in the list. The current code does the decisions primary by CON_CONSDEV
flag that is used for the preferred console. It looks like a
good compromise. And the change seems to be in the right direction.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211122132649.12737-6-pmladek@suse.com
The variable @need_default_console is used to decide whether a newly
registered console should get enabled by default.
The logic is complicated. It can be modified in a register_console()
call. But it is always re-evaluated in the next call by the following
condition:
if (need_default_console || bcon || !console_drivers)
need_default_console = preferred_console < 0;
In short, the value is updated when either of the condition is valid:
+ the value is still, or again, "true"
+ boot/early console is still the first in @console_driver list
+ @console_driver list is empty
The value is updated according to @preferred_console. In particular,
it is set to "false" when a @preferred_console was set by
__add_preferred_console(). This happens when a non-braille console
was added via the command line, device tree, or SPCR.
It far from clear what this all means together. Let's look at
@need_default_console from another angle:
1. The value is "true" by default. It means that it is always set
according to @preferred_console during the first register_console()
call.
By other words, the first register_console() call will register
the console by default only when none non-braille console was defined
via the command line, device tree, or SPCR.
2. The value will always stay "false" when @preferred_console is set.
By other words, try_enable_default_console() will never get called
when a non-braille console is explicitly required.
4. The value might be set to "false" in try_enable_default_console()
when a console with tty binding (driver) gets enabled.
In this case CON_CONSDEV is set as well. It causes that the console
will be inserted as first into the list @console_driver. It might
be either real or boot/early console.
5. The value will be set _back_ to "true" in the next register_console()
call when:
+ The console added by the previous register_console() had been
a boot/early one.
+ The last console has been unregistered in the meantime and
a boot/early console became first in @console_drivers list
again. Or the list became empty.
By other words, the value will stay "false" only when the last
registered console was real, had tty binding, and was not removed
in the mean time.
The main logic looks clear:
+ Consoles are enabled by default only when no one is preferred
via the command line, device tree, or SPCR.
+ By default, any console is enabled until a real console
with tty binding gets registered.
The behavior when the real console with tty binding is later removed
is a bit unclear:
+ By default, any new console is registered again only when there
is no console or the first console in the list is a boot one.
The question is why the code is suddenly happy when a real console
without tty binding is the first in the list. It looks like an overlook
and bug.
Conclusion:
The state of @preferred_console and the first console in @console_driver
list should be enough to decide whether we need to enable the given console
by default.
The rules are simple. New consoles are _not_ enabled by default
when either of the following conditions is true:
+ @preferred_console is set. It means that a non-braille console
is explicitly configured via the command line, device tree, or SPCR.
+ A real console with tty binding is registered. Such a console will
have CON_CONSDEV flag set and will always be the first in
@console_drivers list.
Note:
The new code does not use @bcon variable. The meaning of the variable
is far from clear. The direct check of the first console in the list
makes it more clear that only real console fulfills requirements
of the default console.
Behavior change:
As already discussed above. There was one situation where the original
code worked a strange way. Let's have:
+ console A: real console without tty binding
+ console B: real console with tty binding
and do:
register_console(A); /* 1st step */
register_console(B); /* 2nd step */
unregister_console(B); /* 3rd step */
register_console(B); /* 4th step */
The original code will not register the console B in the 4th step.
@need_default_console is set to "false" in 2nd step. The real console
with tty binding (driver) is then removed in the 3rd step.
But @need_default_console will stay "false" in the 4th step because
there is no boot/early console and @registered_consoles list is not
empty.
The new code will register the console B in the 4th step because
it checks whether the first console has tty binding (->driver)
This behavior change should acceptable:
1. The scenario requires manual intervention (console removal).
The system should boot with the same consoles as before.
2. Console B is registered again probably because the user wants
to use it. The most likely scenario is that the related
module is reloaded.
3. It makes the behavior more consistent and predictable.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211122132649.12737-5-pmladek@suse.com
There is no need to clear @need_default_console when a console
preferred by the command line, device tree, or SPCR, gets enabled.
The code is called only when some non-braille console matched a console
in @console_cmdline array. It means that a non-braille console was added
in __add_preferred_console() and the variable preferred_console is set
to a number >= 0. As a result, @need_default_console is always set to
"false" in the magic condition:
if (need_default_console || bcon || !console_drivers)
need_default_console = preferred_console < 0;
This is one small step in removing the above magic condition
that is hard to follow.
The patch removes one superfluous assignment and should not change
the functionality.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211122132649.12737-4-pmladek@suse.com
The logic around the variable @has_preferred_console made my head
spin many times. Part of the problem is the ambiguous name.
There is the variable @preferred_console. It points to the last
non-braille console in @console_cmdline array. This array contains
consoles preferred via the command line, device tree, or SPCR.
Then there is the variable @has_preferred_console. It is set to
"true" when @preferred_console is enabled or when a console with
tty binding gets enabled by default.
It might get reset back by the magic condition:
if (!has_preferred_console || bcon || !console_drivers)
has_preferred_console = preferred_console >= 0;
It is a puzzle. Dumb explanation is that it gets re-evaluated
when:
+ it was not set before (see above when it gets set)
+ there is still an early console enabled (bcon)
+ there is no console enabled (!console_drivers)
This is still a puzzle.
It gets more clear when we see where the value is checked. The only
meaning of the variable is to decide whether we should try to enable
the new console by default.
Rename the variable according to the single situation where
the value is checked.
The rename requires an inverted logic. Otherwise, it is a simple
search & replace. It does not change the functionality.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/20211122132649.12737-3-pmladek@suse.com
Put the code enabling a console by default into a separate function
called try_enable_default_console().
Rename try_enable_new_console() to try_enable_preferred_console() to
make the purpose of the different variants more clear.
It is a code refactoring without any functional change.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Link: https://lore.kernel.org/r/20211122132649.12737-2-pmladek@suse.com
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Merge tag 'printk-for-5.16-fixup' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux
Pull printk fixes from Petr Mladek:
- Try to flush backtraces from other CPUs also on the local one. This
was a regression caused by printk_safe buffers removal.
- Remove header dependency warning.
* tag 'printk-for-5.16-fixup' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
printk: Remove printk.h inclusion in percpu.h
printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces
