From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 4 Aug 2014 13:31:08 +0000 (+0200)
Subject: perf: Do poll_wait() before checking condition in perf_poll()
X-Git-Tag: omap-for-v3.19/prcm-cleanup~97^2~37
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e708d7ad80737496870fd0b6794704d063fb0cdc;p=pandora-kernel.git

perf: Do poll_wait() before checking condition in perf_poll()

One should first enqueue to the waitqueue and then check for the
condition. If the condition gets true after mutex_unlock() but before
poll_wait() then we lose it and would have wait for another wakeup.

This has been like this since v2.6.31-rc1 commit c7138f37f9 ("perf_counter:
fix perf_poll()"). Before that it was slightly worse. I guess we get enough
wakeups so if we miss here one it doesn't really matter. It is still a
bad example.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1407159068-1478-1-git-send-email-bigeasy@linutronix.de
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

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