linux-kernel - Re: [PATCH 0/4] [GIT PULL] tracing: recursion and compile fixes

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Message-ID: <alpine.DEB.2.00.0904201641570.10097@gandalf.stny.rr.com>
Date:	Mon, 20 Apr 2009 16:44:46 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/4] [GIT PULL] tracing: recursion and compile fixes


On Mon, 20 Apr 2009, Frederic Weisbecker wrote:
> > > 
> > 
> > Hmm, doesn't the trace wakeup test if the runqueue lock is locked or not?
> > 
> > -- Steve
> > 
> 
> 
> Hmm, yes it does but that's not the first time we meet this problem
> (sched switch event tracing recursions by the past). So either the
> test doesn't work well or this is about another lock that
> wake_up_common takes...

Ug, it is the task's rq lock. Not the current rq lock. wakeup takes the 
runqueue lock of the task. The "runqueue_is_locked" only tests the lock of 
current CPU, which is not what we can have.

Thus, the function tracer (gag, and probably the event tracing!) should 
not call wakeups.

-- Steve

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