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Change the method used in hg_intercepts.c to hide from the user, the

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race between mythread_wrapper and the wrapper for pthread_create.  The
previous scheme could lead to false race reports in obscure cases.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11102
This commit is contained in:
Julian Seward 2010-04-12 19:53:05 +00:00
parent 79dc7aab1e
commit 0b869ecf10
2 changed files with 23 additions and 9 deletions
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6
glibc-2.34567-NPTL-helgrind.supp
View File

@ -134,12 +134,6 @@
Helgrind:Race
fun:__lll_*lock_*
}
{
helgrind-glibc2X-112
Helgrind:Race
fun:pthread_create_WRK
fun:pthread_create@*
}
{
helgrind-glibc2X-113
Helgrind:Race

26
helgrind/hg_intercepts.c
View File

@ -193,8 +193,6 @@ static char* lame_strerror ( long err )
/*--- pthread_create, pthread_join, pthread_exit ---*/
/*----------------------------------------------------------------*/
/* Do not rename this function. It contains an unavoidable race and
so is mentioned by name in glibc-*helgrind*.supp. */
static void* mythread_wrapper ( void* xargsV )
{
volatile Word* xargs = (volatile Word*) xargsV;
@ -207,7 +205,17 @@ static void* mythread_wrapper ( void* xargsV )
we're ready because (1) we need to make sure it doesn't exit and
hence deallocate xargs[] while we still need it, and (2) we
don't want either parent nor child to proceed until the tool has
been notified of the child's pthread_t. */
been notified of the child's pthread_t.
Note that parent and child access args[] without a lock,
effectively using args[2] as a spinlock in order to get the
parent to wait until the child passes this point. The parent
disables checking on xargs[] before creating the child and
re-enables it once the child goes past this point, so the user
never sees the race. The previous approach (suppressing the
resulting error) was flawed, because it could leave shadow
memory for args[] in a state in which subsequent use of it by
the parent would report further races. */
xargs[2] = 0;
/* Now we can no longer safely use xargs[]. */
return (void*) fn( (void*)arg );
@ -237,6 +245,14 @@ static int pthread_create_WRK(pthread_t *thread, const pthread_attr_t *attr,
xargs[0] = (Word)start;
xargs[1] = (Word)arg;
xargs[2] = 1; /* serves as a spinlock -- sigh */
/* Disable checking on the spinlock and the two words used to
convey args to the child. Basically we need to make it appear
as if the child never accessed this area, since merely
suppressing the resulting races does not address the issue that
that piece of the parent's stack winds up in the "wrong" state
and therefore may give rise to mysterious races when the parent
comes to re-use this piece of stack in some other frame. */
VALGRIND_HG_DISABLE_CHECKING(&xargs, sizeof(xargs));
CALL_FN_W_WWWW(ret, fn, thread,attr,mythread_wrapper,&xargs[0]);
@ -256,6 +272,10 @@ static int pthread_create_WRK(pthread_t *thread, const pthread_attr_t *attr,
DO_PthAPIerror( "pthread_create", ret );
}
/* Reenable checking on the area previously used to communicate
with the child. */
VALGRIND_HG_ENABLE_CHECKING(&xargs, sizeof(xargs));
if (TRACE_PTH_FNS) {
fprintf(stderr, " :: pth_create -> %d >>\n", ret);
}