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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>
This commit is contained in:
Ingo Molnar 2009-09-22 14:44:11 +02:00
parent 979f693def
commit edaac8e316
1 changed files with 9 additions and 1 deletions
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10
lib/ratelimit.c
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@ -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;