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

[Thomas Gleixner]

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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