linux-kernel - Re: [patch 0/3] futex/rtmutex: Fix issues exposed by trinity

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Date:	Tue, 13 May 2014 11:08:47 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Darren Hart <dvhart@...ux.intel.com>
cc:	LKML <linux-kernel@...r.kernel.org>, Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <darren@...art.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Clark Williams <williams@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Roland McGrath <roland@...k.frob.com>,
	Carlos ODonell <carlos@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [patch 0/3] futex/rtmutex: Fix issues exposed by trinity

On Mon, 12 May 2014, Darren Hart wrote:
> On Mon, May 12, 2014 at 08:45:32PM -0000, Thomas Gleixner wrote:
> >    strace tells me:
> > 
> >    futex(0x600e00, FUTEX_LOCK_PI_PRIVATE, 1) = -1 EINVAL (Invalid argument)
> > 
> >    but the return value of pthread_mutex_lock() is 0
> 
> So something is clearly wrong there - however, were you looking at the comments
> (sorry, I mean the C code), or the implementation (all the ASM)? The only way
> I've been able to be sure in the past is to delete the ASM files and recompile
> using the C files. Hopefully we'll be able to drop all the ASM in the pthread
> calls soonish (measured in years in glibc development time scales).... sigh.

The C implementation does:

	    if (INTERNAL_SYSCALL_ERROR_P (e, __err)
		&& (INTERNAL_SYSCALL_ERRNO (e, __err) == ESRCH
		    || INTERNAL_SYSCALL_ERRNO (e, __err) == EDEADLK))
	      {
		assert (INTERNAL_SYSCALL_ERRNO (e, __err) != EDEADLK
			|| (kind != PTHREAD_MUTEX_ERRORCHECK_NP
			    && kind != PTHREAD_MUTEX_RECURSIVE_NP));
		/* ESRCH can happen only for non-robust PI mutexes where
		   the owner of the lock died.  */
		assert (INTERNAL_SYSCALL_ERRNO (e, __err) != ESRCH || !robust);

		/* Delay the thread indefinitely.  */
		while (1)
		  pause_not_cancel ();
	      }

So anything else than ESRCH and EDEADLK is ignored and then the thing
happily returns 0 at the end. Unlock is the same:

	{
	  int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
	  int private = (robust
			 ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
			 : PTHREAD_MUTEX_PSHARED (mutex));
	  INTERNAL_SYSCALL_DECL (__err);
	  INTERNAL_SYSCALL (futex, __err, 2, &mutex->__data.__lock,
			    __lll_private_flag (FUTEX_UNLOCK_PI, private));
	}

Quality stuff that.

Thanks,

	tglx

 
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