Commit 190320c3 authored Jul 30, 2012 by Vikram Mulukutla Committed by Linus Torvalds Jul 30, 2012

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>

parent 6c55845e

kernel/panic.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -74,6 +74,14 @@ void panic(const char *fmt, ...)
		long i, i_next = 0;
		int state = 0;

		/*
		* Disable local interrupts. This will prevent panic_smp_self_stop
		* from deadlocking the first cpu that invokes the panic, since
		* there is nothing to prevent an interrupt handler (that runs
		* after the panic_lock is acquired) from invoking panic again.
		*/
		local_irq_disable();

		/*
		* It's possible to come here directly from a panic-assertion and
		* not have preempt disabled. Some functions called from here want