Commit edaac8e3 authored Sep 22, 2009 by Ingo Molnar

ratelimit: Fix/allow use in atomic contexts



I'd like to use printk_ratelimit() in NMI context, but it's not
robust right now due to spinlock usage in lib/ratelimit.c. If an
NMI is unlucky enough to hit just that spot we might lock up trying
to take the spinlock again.

Fix that by using a trylock variant. If we contend on that lock we
can genuinely skip the message because the state is just being
accessed by another CPU (or by this CPU).

( We could use atomics for the suppressed messages field, but
  i doubt it matters in practice and it makes the code heavier. )

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David S. Miller <davem@davemloft.net>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 979f693d

lib/ratelimit.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -28,7 +28,15 @@ int __ratelimit(struct ratelimit_state *rs)
		if (!rs->interval)
		return 1;

		spin_lock_irqsave(&rs->lock, flags);
		/*
		* If we contend on this state's lock then almost
		* by definition we are too busy to print a message,
		* in addition to the one that will be printed by
		* the entity that is holding the lock already:
		*/
		if (!spin_trylock_irqsave(&rs->lock, flags))
		return 1;

		if (!rs->begin)
		rs->begin = jiffies;

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