Re: [PING][PATCH] Correct mutex type check for disable lock elision via pthread_mutexattr_settype call

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

ping.

ok to commit?

On 04/08/2014 02:08 PM, Stefan Liebler wrote:
> ping!
> On 04/01/2014 10:29 AM, Stefan Liebler wrote:
> > Hi,
> >
> > if glibc is build with --enable-lock-elision=yes,
> > all default mutexes are elided (only for supported architectures).
> > Someone can disable the elision for one specific mutex with
> > a call to pthread_mutexattr_settype.
> > Currently you can specify either PTHREAD_MUTEX_NORMAL or
> > PTHREAD_MUTEX_DEFAULT, because they are both defined to 0.
> > The function checks for type PTHREAD_MUTEX_DEFAULT
> > and then disables elision.
> >
> > For correctness, the function should check against PTHREAD_MUTEX_NORMAL!
> > According to POSIX, PTHREAD_MUTEX_NORMAL shall deadlock if a thread
> > tries to relock a mutex without first unlocking it.
> > In case of PTHREAD_MUTEX_DEFAULT, the behavior is undefined.
> > Thus the mutex can be elided with PTHREAD_MUTEX_DEFAULT, but not with
> > PTHREAD_MUTEX_NORMAL.
> > The same can be read in the lock elision implementation guidelines
> > (https://sourceware.org/glibc/wiki/LockElisionGuide).
> >
> > Bye.
> >
> > ---
> > 2014-04-01  Stefan Liebler  <stli@linux.vnet.ibm.com>
> >
> >      * nptl/pthread_mutexattr_settype.c
> >      (__pthread_mutexattr_settype):
> >      Disable lock elision for PTHREAD_MUTEX_NORMAL.
> > ---