printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces

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printk from NMI context relies on irq work being raised on the local CPU
to print to console. This can be a problem if the NMI was raised by a
lockup detector to print lockup stack and regs, because the CPU may not
enable irqs (because it is locked up).

Introduce printk_trigger_flush() that can be called another CPU to try
to get those messages to the console, call that where printk_safe_flush
was previously called.

Fixes: 93d102f094 ("printk: remove safe buffers")
Cc: stable@vger.kernel.org # 5.15
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20211107045116.1754411-1-npiggin@gmail.com

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Nicholas Piggin 2021-11-07 14:51:16 +10:00 • committed by Petr Mladek

parent 26d1982fd1

commit 5d5e4522a7

4 changed files with 21 additions and 0 deletions

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6

arch/powerpc/kernel/watchdog.c

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4

include/linux/printk.h

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5

kernel/printk/printk.c

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6

lib/nmi_backtrace.c

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