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Fix bugs in powerpc pthread_once.

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Ref gcc.gnu.org/bugzilla/show_bug.cgi?id=52839#c10

Release barriers are needed to ensure that any memory written by
init_routine is seen by other threads before *once_control changes.
In the case of clear_once_control we need to flush any partially
written state.
This commit is contained in:
Alan Modra 2012-09-25 16:30:06 -05:00 committed by Ryan S. Arnold
parent 1c530d0244
commit 7e2fca8dd2
2 changed files with 24 additions and 5 deletions
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8
ChangeLog
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@ -1,3 +1,11 @@
2012-09-25 Alan Modra <amodra@gmail.com>
* sysdeps/unix/sysv/linux/powerpc/pthread_once.c (__pthread_once):
Add release barrier before setting once_control to say
initialisation is done. Add hints on lwarx. Use macro in
place of isync.
(clear_once_control): Add release barrier.
2012-09-25 Joseph Myers <joseph@codesourcery.com>
[BZ #13629]

21
nptl/sysdeps/unix/sysv/linux/powerpc/pthread_once.c
View File

@ -28,6 +28,7 @@ clear_once_control (void *arg)
{
pthread_once_t *once_control = (pthread_once_t *) arg;
__asm __volatile (__lll_rel_instr);
*once_control = 0;
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
}
@ -47,15 +48,15 @@ __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
oldval = *once_control;
if ((oldval & 2) == 0)
*once_control = newval;
Do this atomically.
Do this atomically with an acquire barrier.
*/
newval = __fork_generation | 1;
__asm __volatile ("1: lwarx %0,0,%3\n"
__asm __volatile ("1: lwarx %0,0,%3" MUTEX_HINT_ACQ "\n"
" andi. %1,%0,2\n"
" bne 2f\n"
" stwcx. %4,0,%3\n"
" bne 1b\n"
"2: isync"
"2: " __lll_acq_instr
: "=&r" (oldval), "=&r" (tmp), "=m" (*once_control)
: "r" (once_control), "r" (newval), "m" (*once_control)
: "cr0");
@ -87,8 +88,18 @@ __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
pthread_cleanup_pop (0);
/* Add one to *once_control to take the bottom 2 bits from 01 to 10. */
atomic_increment (once_control);
/* Add one to *once_control to take the bottom 2 bits from 01 to 10.
A release barrier is needed to ensure memory written by init_routine
is seen in other threads before *once_control changes. */
int tmp;
__asm __volatile (__lll_rel_instr "\n"
"1: lwarx %0,0,%2" MUTEX_HINT_REL "\n"
" addi %0,%0,1\n"
" stwcx. %0,0,%2\n"
" bne- 1b"
: "=&b" (tmp), "=m" (*once_control)
: "r" (once_control), "m" (*once_control)
: "cr0");
/* Wake up all other threads. */
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);