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panic: fix a possible deadlock in panic()
panic_lock is meant to ensure that panic processing takes place only on one cpu; if any of the other cpus encounter a panic, they will spin waiting to be shut down. However, this causes a regression in this scenario: 1. Cpu 0 encounters a panic and acquires the panic_lock and proceeds with the panic processing. 2. There is an interrupt on cpu 0 that also encounters an error condition and invokes panic. 3. This second invocation fails to acquire the panic_lock and enters the infinite while loop in panic_smp_self_stop. Thus all panic processing is stopped, and the cpu is stuck for eternity in the while(1) inside panic_smp_self_stop. To address this, disable local interrupts with local_irq_disable before acquiring the panic_lock. This will prevent interrupt handlers from executing during the panic processing, thus avoiding this particular problem. Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org> Reviewed-by: Stephen Boyd <sboyd@codeaurora.org> Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -74,6 +74,14 @@ void panic(const char *fmt, ...)
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long i, i_next = 0;
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int state = 0;
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/*
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* Disable local interrupts. This will prevent panic_smp_self_stop
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* from deadlocking the first cpu that invokes the panic, since
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* there is nothing to prevent an interrupt handler (that runs
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* after the panic_lock is acquired) from invoking panic again.
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*/
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local_irq_disable();
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/*
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* It's possible to come here directly from a panic-assertion and
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* not have preempt disabled. Some functions called from here want
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