linux-kernel - Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand unprotected when accessed by /proc)

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Message-ID: <alpine.DEB.2.10.1406212153300.5170@nanos>
Date:	Sat, 21 Jun 2014 21:54:59 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: safety of *mutex_unlock() (Was: [BUG] signal: sighand unprotected
 when accessed by /proc)

On Wed, 18 Jun 2014, Steven Rostedt wrote:

> On Wed, 18 Jun 2014 18:43:59 +0200
> Oleg Nesterov <oleg@...hat.com> wrote:
> 
>  
> > And (contrary to what I said initially) we can rely on this because -rt
> > converts spinlock_t into rt_mutex ?
> 
> Correct. Because if spinlock_t has this behavior, rt_mutex must have it
> too, otherwise -rt will suffer greatly from that. Who knows, maybe this
> will fix some strange bug reports that we have had in the past.

Indeed. I found a few backtraces from Carstens test farm, where stuff
explodes in the slowpath raw_spin_unlock call. Happens once a year or
never ...

Thanks,

	tglx
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