From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Thu, 17 May 2012 19:19:46 +0000 (+0200)
Subject: sched/rt: Fix lockdep annotation within find_lock_lowest_rq()
X-Git-Tag: v3.5-rc2~2^2~4
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=7f1b43936f0ecad14770634c021cf4a929aec74d;p=pandora-kernel.git

sched/rt: Fix lockdep annotation within find_lock_lowest_rq()

Roland Dreier reported spurious, hard to trigger lockdep warnings
within the scheduler - without any real lockup.

This bit gives us the right clue:

> [89945.640512]  [<ffffffff8103fa1a>] double_lock_balance+0x5a/0x90
> [89945.640568]  [<ffffffff8104c546>] push_rt_task+0xc6/0x290

if you look at that code you'll find the double_lock_balance() in
question is the one in find_lock_lowest_rq() [yay for inlining].

Now find_lock_lowest_rq() has a bug.. it fails to use
double_unlock_balance() in one exit path, if this results in a retry in
push_rt_task() we'll call double_lock_balance() again, at which point
we'll run into said lockdep confusion.

Reported-by: Roland Dreier <roland@kernel.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1337282386.4281.77.camel@twins
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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