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kdb: Make kdb_printf() console handling more robust

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While rounding up CPUs via NMIs, its possible that a rounded up CPU
maybe holding a console port lock leading to kgdb master CPU stuck in
a deadlock during invocation of console write operations. A similar
deadlock could also be possible while using synchronous breakpoints.

So in order to avoid such a deadlock, set oops_in_progress to encourage
the console drivers to disregard their internal spin locks: in the
current calling context the risk of deadlock is a bigger problem than
risks due to re-entering the console driver. We operate directly on
oops_in_progress rather than using bust_spinlocks() because the calls
bust_spinlocks() makes on exit are not appropriate for this calling
context.

Suggested-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/1591264879-25920-4-git-send-email-sumit.garg@linaro.org
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
This commit is contained in:
Sumit Garg 2020-06-04 15:31:18 +05:30 committed by Daniel Thompson
parent e8857288bb
commit 2a78b85b70
1 changed files with 11 additions and 0 deletions
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11
kernel/debug/kdb/kdb_io.c
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@ -562,7 +562,18 @@ static void kdb_msg_write(const char *msg, int msg_len)
for_each_console(c) {
if (!(c->flags & CON_ENABLED))
continue;
/*
* Set oops_in_progress to encourage the console drivers to
* disregard their internal spin locks: in the current calling
* context the risk of deadlock is a bigger problem than risks
* due to re-entering the console driver. We operate directly on
* oops_in_progress rather than using bust_spinlocks() because
* the calls bust_spinlocks() makes on exit are not appropriate
* for this calling context.
*/
++oops_in_progress;
c->write(c, msg, msg_len);
--oops_in_progress;
touch_nmi_watchdog();
}
}