[m-rev.] For review: Workaround Linux NTPL TSX bug (Mercury Bug: 334)
paul at bone.id.au
Fri Jun 27 17:54:14 AEST 2014
On Fri, Jun 27, 2014 at 05:16:09PM +1000, Peter Wang wrote:
> On Fri, 27 Jun 2014 16:18:26 +1000, Paul Bone <paul at bone.id.au> wrote:
> > On Fri, Jun 27, 2014 at 03:33:46PM +1000, Peter Wang wrote:
> > > On Fri, 27 Jun 2014 11:27:40 +1000, Paul Bone <paul at bone.id.au> wrote:
> > > >
> > > > Of course my change here is only a workaround. The real fix is patching
> > > > glibc.
> > >
> > > Well, I prefer you do not commit it. If it's just to continue your
> > > development, I think you could rebuild glibc with --disable-lock-elision
> > > and LD_PRELOAD libpthread?
> > What if other users have the same error? This affects all
> > asm_fast.gc.par.stseg grades. I can't resonably ask other users, including
> > yourself, either to buy a processor without this extension or to always use
> > an older version of glibc.
> I guess I'm expecting that it to be fixed one way or another, in due
> time, if more popular Boehm GC-using software is affected.
I've no intention of waiting the unspecified amount of time it will take for
1) the bug to be acknowledged*
2) the bug to be patched
3) the patches to trickle down to actually be installed on people's
*: I don't think that the developers of glibc and/or Andi will actually be
any worse than any other developer in this regard. I'm not making a
personal attack I'm just cynical.
> > > Otherwise, from what I can tell, calling pthread_mutexattr_settype with
> > > PTHREAD_MUTEX_DEFAULT (or maybe PTHREAD_MUTEX_NORMAL) is enough to
> > > disable lock elision, which is the same type of mutex as for
> > > PTHREAD_MUTEX_INITIALIZER. You don't need to test the glibc version.
> > Are you saying that PTHREAD_MUTEX_DEFAULT and/or PTHREAD_MUTEX_NORMAL also
> > disable elision?
> PTHREAD_MUTEX_DEFAULT for glibc-2.19
> PTHREAD_MUTEX_NORMAL for unreleased versions
Okay, that's certainly simpler. I'm happy to remove all the conditional
compilation and testing of glibc's version and always use
The man page for pthread_mutexattr_settype says that PTHREAD_MUTEX_NORMAL
locks will deadlock if you try and lock them a second time from the same
thread, which (AIUI) an elision implementation can't handle. So this is
probably the most reliable incase in the future PTHREAD_MUTEX_DEFAULT is
ever assigned to some other behaviour.
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