Re: Disable all lock elision unless --enable-lock-elision=yes

[Thomas Backlund <tmb at mageia dot org>]

Carlos O'Donell skrev den 29.9.2014 17:05:
> On 09/27/2014 02:10 PM, Andi Kleen wrote:
> > Hi Carlos,
> >
> > On Sat, Sep 27, 2014 at 12:40:28AM -0400, Carlos O'Donell wrote:
> > > Andi.
> > >
> > > The rwlock elision support you added in 2014-06-13
> > > appears to unconditionally enable elision for rwlock's
> > > if the RTM-bit indicates TSX is present. That isn't what
> > > we do for mutexes, and isn't very conservative in that
> > > case.
> > >
> > > Did I read the code right?
> >
> > You're right. It should have been disabled in this case.
> >
> > Patch looks good to me.
>
> Andi,
>
> Thanks. I'll get that checked in shortly. I just wanted to make
> sure that we weren't doing it for any other reason.
>
> I'll adjust the wording of the configure switch to indicate it
> is for all elision usage in the library.


We seem to hit problems with this in Mageia when the installer runs :/

Building glibc with the patch applied:
http://svnweb.mageia.org/packages/cauldron/glibc/current/SOURCES/glibc-2.20-disable-all-lock-elision-unless--enable-lock-elision-is-yes.patch?view=markup&pathrev=731421

and dropping "--enable-lock-elision" from configure we hit SIGILL
on an old Intel E8400 CPU running x86_64 (and this with old 20131009 
firmware) and some others:


Program received signal SIGILL, Illegal instruction.
__GI___pthread_rwlock_unlock (rwlock=rwlock@entry=0x7ffff40dcd00 
<_globalCtx.5791>) at pthread_rwlock_unlock.c:34
34        if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
(gdb) bt
#0  0x00007ffff6ca0192 in __GI___pthread_rwlock_unlock 
(rwlock=rwlock@entry=0x7ffff40dcd00 <_globalCtx.5791>) at 
pthread_rwlock_unlock.c:34
#1  0x00007ffff3ec59a4 in rpmlog (ctx=0x7ffff40dcd00 <_globalCtx.5791>) 
at rpmlog.c:49
#2  0x00007ffff3ec59a4 in rpmlog (code=code@entry=4, fmt=0x7ffff4131db6 
"%s created as %s\n") at rpmlog.c:287
#3  0x00007ffff410cd4a in rpmPackageFilesInstall (suffix=<optimized 
out>, action=FA_ALTNAME, fi=0x81d9470, path=<synthetic pointer>) at 
fsm.c:756
#4  0x00007ffff410cd4a in rpmPackageFilesInstall (ts=<optimized out>, 
te=<optimized out>, files=<optimized out>, psm=psm@entry=0x5a877e0, 
failedFile=failedFile@entry=0x7fffffffd848) at fsm.c:948
#5  0x00007ffff4110725 in rpmpsmUnpack (psm=psm@entry=0x5a877e0) at 
psm.c:662
#6  0x00007ffff4110d8c in rpmpsmRun (psm=0x5a877e0, ts=0x910ca60) at 
psm.c:741
#7  0x00007ffff4110d8c in rpmpsmRun (ts=0x910ca60, 
te=te@entry=0x9464300, goal=goal@entry=PKG_INSTALL) at psm.c:842
#8  0x00007ffff4122dcc in rpmteProcess (te=0x9464300, goal=PKG_INSTALL) 
at rpmte.c:757
#9  0x00007ffff4128e7a in rpmtsRun (ts=<optimized out>) at 
transaction.c:1376
#10 0x00007ffff4128e7a in rpmtsRun (ts=0x0, okProbs=okProbs@entry=0x0, 
ignoreSet=153090448) at transaction.c:1491
#11 0x00007ffff4355530 in XS_URPM__Transaction_run (my_perl=<optimized 
out>, cv=<optimized out>) at URPM.xs:2732
#12 0x00007ffff7aee60b in Perl_pp_entersub (my_perl=0x603010) at 
pp_hot.c:2794
#13 0x00007ffff7ae6fd6 in Perl_runops_standard (my_perl=0x603010) at 
run.c:42
#14 0x00007ffff7a78ded in perl_run (oldscope=1, my_perl=0x603010) at 
perl.c:2451
#15 0x00007ffff7a78ded in perl_run (my_perl=0x603010) at perl.c:2372
#16 0x0000000000400ea9 in main (argc=11, argv=0x7fffffffdf38, 
env=0x7fffffffdf98) at perlmain.c:114


--

Thomas