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powerpc/crash: Use NMI context for printk when starting to crash

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Currently, if printk lock (logbuf_lock) is held by other thread during
crash, there is a chance of deadlocking the crash on next printk, and
blocking a possibly desired kdump.

At the start of default_machine_crash_shutdown, make printk enter
NMI context, as it will use per-cpu buffers to store the message,
and avoid locking logbuf_lock.

Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200512214533.93878-1-leobras.c@gmail.com
This commit is contained in:
Leonardo Bras 2020-05-12 18:45:35 -03:00 committed by Michael Ellerman
parent b6eca183e2
commit af2876b501
1 changed files with 3 additions and 0 deletions
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3
arch/powerpc/kexec/crash.c
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@ -311,6 +311,9 @@ void default_machine_crash_shutdown(struct pt_regs *regs)
unsigned int i;
int (*old_handler)(struct pt_regs *regs);
/* Avoid hardlocking with irresponsive CPU holding logbuf_lock */
printk_nmi_enter();
/*
* This function is only called after the system
* has panicked or is otherwise in a critical state.