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Petr Mladek 7dca9fa41c printk/console: Allow to disable console output by using console="" or console=null 
commit 3cffa06aeef7ece30f6b5ac0ea51f264e8fea4d0 upstream.

The commit 48021f98130880dd74 ("printk: handle blank console arguments
passed in.") prevented crash caused by empty console= parameter value.

Unfortunately, this value is widely used on Chromebooks to disable
the console output. The above commit caused performance regression
because the messages were pushed on slow console even though nobody
was watching it.

Use ttynull driver explicitly for console="" and console=null
parameters. It has been created for exactly this purpose.

It causes that preferred_console is set. As a result, ttySX and ttyX
are not used as a fallback. And only ttynull console gets registered by
default.

It still allows to register other consoles either by additional console=
parameters or SPCR. It prevents regression because it worked this way even
before. Also it is a sane semantic. Preventing output on all consoles
should be done another way, for example, by introducing mute_console
parameter.

Link: https://lore.kernel.org/r/20201006025935.GA597@jagdpanzerIV.localdomain
Suggested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20201111135450.11214-3-pmladek@suse.com
Cc: Yi Fan <yfa@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-11-12 13:18:02 +01:00
..
bpf
bpf: Fix integer overflow in prealloc_elems_and_freelist()
2021-10-17 10:05:39 +02:00
configs
config: android: enable CONFIG_SECCOMP
2016-10-11 15:06:32 -07:00
debug
kdb: Make memory allocations more robust
2021-03-03 17:44:31 +01:00
events
events: Reuse value read using READ_ONCE instead of re-reading it
2021-09-22 11:43:09 +02:00
gcov
gcov: add support for GCC 10.1
2020-09-23 08:46:14 +02:00
irq
genirq: Disable interrupts for force threaded handlers
2021-03-24 10:59:26 +01:00
livepatch
livepatch/module: make TAINT_LIVEPATCH module-specific
2016-08-26 14:42:08 +02:00
locking
futex: Handle early deadlock return correctly
2021-03-30 14:41:42 +02:00
power
PM: hibernate: remove the bogus call to get_gendisk() in software_resume()
2020-10-29 09:05:43 +01:00
printk
printk/console: Allow to disable console output by using console="" or console=null
2021-11-12 13:18:02 +01:00
rcu
rcuperf: Fix cleanup path for invalid perf_type strings
2019-05-31 06:48:30 -07:00
sched
cpufreq: schedutil: Use kobject release() method to free sugov_tunables
2021-10-06 10:23:41 +02:00
time
kernel, fs: Introduce and use set_restart_fn() and arch_set_restart_data()
2021-03-24 10:59:25 +01:00
trace
tracing: Have all levels of checks prevent recursion
2021-10-27 09:34:01 +02:00
.gitignore
…
acct.c
kernel/acct.c: fix the acct->needcheck check in check_free_space()
2018-01-10 09:29:51 +01:00
async.c
kernel/async.c: revert "async: simplify lowest_in_progress()"
2018-02-17 13:21:18 +01:00
audit_fsnotify.c
…
audit_tree.c
…
audit_watch.c
audit: CONFIG_CHANGE don't log internal bookkeeping as an event
2020-10-01 20:40:07 +02:00
audit.c
audit: fix a net reference leak in audit_list_rules_send()
2021-04-07 12:05:41 +02:00
audit.h
audit: fix a net reference leak in audit_list_rules_send()
2021-04-07 12:05:41 +02:00
auditfilter.c
audit: fix a net reference leak in audit_list_rules_send()
2021-04-07 12:05:41 +02:00
auditsc.c
audit: print empty EXECVE args
2019-11-28 18:28:55 +01:00
backtracetest.c
…
bounds.c
kbuild: fix kernel/bounds.c 'W=1' warning
2018-11-13 11:16:57 -08:00
capability.c
ptrace: Capture the ptracer's creds not PT_PTRACE_CAP
2017-01-06 10:40:13 +01:00
cgroup_freezer.c
…
cgroup_pids.c
cgroup: pids: use atomic64_t for pids->limit
2019-12-21 10:42:02 +01:00
cgroup.c
cgroup1: don't allow '\n' in renaming
2021-06-16 11:36:34 +02:00
compat.c
…
configs.c
…
context_tracking.c
…
cpu_pm.c
kernel/cpu_pm: Fix uninitted local in cpu_pm
2020-06-20 10:24:21 +02:00
cpu.c
kernel/cpu: add arch override for clear_tasks_mm_cpumask() mm handling
2020-12-29 13:44:50 +01:00
cpuset.c
sched/cpuset/pm: Fix cpuset vs. suspend-resume bugs
2017-10-12 11:51:25 +02:00
crash_dump.c
…
cred.c
memcg: account security cred as well to kmemcg
2020-01-12 11:24:13 +01:00
delayacct.c
…
dma.c
…
exec_domain.c
…
exit.c
futex: Mark the begin of futex exit explicitly
2021-02-03 23:19:49 +01:00
extable.c
kernel/extable.c: mark core_kernel_text notrace
2017-07-21 07:42:21 +02:00
fork.c
mm/hugetlb: initialize hugetlb_usage in mm_init
2021-09-22 11:43:08 +02:00
freezer.c
freezer, oom: check TIF_MEMDIE on the correct task
2016-07-28 16:07:41 -07:00
futex.c
mm, futex: fix shared futex pgoff on shmem huge page
2021-07-11 12:46:40 +02:00
groups.c
kernel: make groups_sort calling a responsibility group_info allocators
2018-01-10 09:29:52 +01:00
hung_task.c
kernel: hung_task.c: disable on suspend
2019-04-20 09:07:52 +02:00
irq_work.c
…
jump_label.c
jump_label: Invoke jump_label_test() via early_initcall()
2017-12-14 09:28:24 +01:00
kallsyms.c
…
kcmp.c
…
Kconfig.freezer
…
Kconfig.hz
…
Kconfig.locks
…
Kconfig.preempt
…
kcov.c
kcov: ensure irq code sees a valid area
2018-08-03 07:55:12 +02:00
kexec_core.c
objtool, x86: Add several functions and files to the objtool whitelist
2018-06-05 10:28:57 +02:00
kexec_file.c
kernel: kexec_file: fix error return code of kexec_calculate_store_digests()
2021-05-22 10:40:31 +02:00
kexec_internal.h
…
kexec.c
kexec: allow architectures to override boot mapping
2016-08-02 19:35:27 -04:00
kmod.c
usermodehelper: reset umask to default before executing user process
2020-10-14 09:48:14 +02:00
kprobes.c
kretprobe: Avoid re-registration of the same kretprobe earlier
2021-02-10 09:09:25 +01:00
ksysfs.c
kexec: add a kexec_crash_loaded() function
2016-08-02 19:35:30 -04:00
kthread.c
kthread: prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync()
2021-07-11 12:46:41 +02:00
latencytop.c
…
Makefile
elfcore: fix building with clang
2021-02-10 09:09:25 +01:00
membarrier.c
Fix: Disable sys_membarrier when nohz_full is enabled
2017-03-12 06:41:45 +01:00
memremap.c
mm, devm_memremap_pages: kill mapping "System RAM" support
2019-01-13 10:03:51 +01:00
module_signing.c
…
module-internal.h
…
module.c
module: Ignore _GLOBAL_OFFSET_TABLE_ when warning for undefined symbols
2021-03-03 17:44:44 +01:00
notifier.c
x86/mm: split vmalloc_sync_all()
2020-04-02 17:20:26 +02:00
nsproxy.c
…
padata.c
padata: purge get_cpu and reorder_via_wq from padata_do_serial
2020-05-27 16:41:53 +02:00
panic.c
panic: ensure preemption is disabled during panic()
2019-10-17 13:42:25 -07:00
params.c
…
pid_namespace.c
memcg: enable accounting for pids in nested pid namespaces
2021-09-22 11:43:08 +02:00
pid.c
pidns: disable pid allocation if pid_ns_prepare_proc() is failed in alloc_pid()
2018-04-13 19:47:53 +02:00
profile.c
profiling: fix shift-out-of-bounds bugs
2021-09-26 13:36:18 +02:00
ptrace.c
ptrace: make ptrace() fail if the tracee changed its pid unexpectedly
2021-05-26 11:29:06 +02:00
range.c
…
reboot.c
reboot: fix overflow parsing reboot cpu number
2020-11-18 18:26:32 +01:00
relay.c
kernel/relay.c: fix memleak on destroy relay channel
2020-08-26 10:29:03 +02:00
resource.c
resource: fix integer overflow at reallocation
2018-04-24 09:34:09 +02:00
seccomp.c
seccomp: Add missing return in non-void function
2021-03-03 17:44:43 +01:00
signal.c
signal: Extend exec_id to 64bits
2020-04-24 07:58:54 +02:00
smp.c
cpu/hotplug: Fix SMT supported evaluation
2018-08-15 18:14:53 +02:00
smpboot.c
kthread/smpboot: do not park in kthread_create_on_cpu()
2016-10-11 15:06:33 -07:00
smpboot.h
…
softirq.c
Mark HI and TASKLET softirq synchronous
2018-08-15 18:14:42 +02:00
stacktrace.c
stacktrace, lockdep: Fix address, newline ugliness
2017-02-14 15:25:42 -08:00
stop_machine.c
stop_machine: Use raw spinlocks
2018-08-03 07:55:24 +02:00
sys_ni.c
x86/pkeys: Fix pkeys build breakage for some non-x86 arches
2016-09-13 14:41:36 +02:00
sys.c
prctl: allow to setup brk for et_dyn executables
2021-09-26 13:36:18 +02:00
sysctl_binary.c
…
sysctl.c
sched/rt: Show the 'sched_rr_timeslice' SCHED_RR timeslice tuning knob in milliseconds
2020-07-09 09:35:55 +02:00
task_work.c
task_work: use READ_ONCE/lockless_dereference, avoid pi_lock if !task_works
2016-08-02 19:35:02 -04:00
taskstats.c
taskstats: fix data-race
2020-01-12 11:24:12 +01:00
test_kprobes.c
…
torture.c
torture: Convert torture_shutdown() to hrtimer
2016-08-22 10:01:49 -07:00
tracepoint.c
tracepoint: Do not fail unregistering a probe due to memory failure
2021-03-03 17:44:38 +01:00
tsacct.c
…
ucount.c
kernel/ucount.c: mark user_header with kmemleak_ignore()
2017-06-17 06:41:51 +02:00
uid16.c
kernel: make groups_sort calling a responsibility group_info allocators
2018-01-10 09:29:52 +01:00
up.c
smp: Add function to execute a function synchronously on a CPU
2016-09-05 13:52:39 +02:00
user_namespace.c
userns: move user access out of the mutex
2018-09-09 20:01:24 +02:00
user-return-notifier.c
…
user.c
…
utsname_sysctl.c
sys: don't hold uts_sem while accessing userspace memory
2018-09-09 20:01:24 +02:00
utsname.c
Merge branch 'nsfs-ioctls' into HEAD
2016-09-22 20:00:36 -05:00
watchdog_hld.c
kernel/watchdog: prevent false hardlockup on overloaded system
2017-06-17 06:41:57 +02:00
watchdog.c
kernel/watchdog: prevent false hardlockup on overloaded system
2017-06-17 06:41:57 +02:00
workqueue_internal.h
workqueue: Fix NULL pointer dereference
2017-11-15 15:53:17 +01:00
workqueue.c
workqueue: fix UAF in pwq_unbound_release_workfn()
2021-08-04 11:58:01 +02:00