47677f2edc
This patch fixes both sem_wait and sem_timedwait cancellation point for
uncontended case. In this scenario only atomics are involved and thus
the futex cancellable call is not issue and a pending cancellation signal
is not handled.
The fix is straighforward by calling pthread_testcancel is both function
start. Although it would be simpler to call CANCELLATION_P directly, I
decided to add an internal pthread_testcancel alias and use it to export
less internal implementation on such function. A possible change on
how pthread_testcancel is internally implemented would lead to either
continue to force use CANCELLATION_P or to adjust its every use.
GLIBC testcase also does have tests for uncontended cases, test-cancel12
and test-cancel14.c, however both are flawed by adding another
cancellation point just after thread pthread_cleanup_pop:
47 static void *
48 tf (void *arg)
49 {
50 pthread_cleanup_push (cleanup, NULL);
51
52 int e = pthread_barrier_wait (&bar);
53 if (e != 0 && e != PTHREAD_BARRIER_SERIAL_THREAD)
54 {
55 puts ("tf: 1st barrier_wait failed");
56 exit (1);
57 }
58
59 /* This call should block and be cancelable. */
60 sem_wait (&sem);
61
62 pthread_cleanup_pop (0);
63
64 puts ("sem_wait returned");
65
66 return NULL;
67 }
So sem_{timed}wait does not act on cancellation, pthread_cleanup_pop executes
'cleanup' and then 'puts' acts on cancellation. Since pthread_cleanup_pop
removed the clean-up handler, it will ran only once and thus it won't accuse
an error to indicate sem_wait has not acted on the cancellation signal.
This patch also fixes this behavior by removing the cancellation point 'puts'.
It also adds some cleanup on all sem_{timed}wait cancel tests.
It partially fixes BZ #18243. Checked on x86_64.
[BZ #18243]
* nptl/pthreadP.h (__pthread_testcancel): Add prototype and hidden_proto.
* nptl/pthread_testcancel.c (pthread_cancel): Add internal aliais
definition.
* nptl/sem_timedwait.c (sem_timedwait): Add cancellation check for
uncontended case.
* nptl/sem_wait.c (__new_sem_wait): Likewise.
* nptl/tst-cancel12.c (cleanup): Remove wrong cancellation point.
(tf): Fix check for uncontended case.
(do_test): Likewise.
* nptl/tst-cancel13.c (cleanup): Remove wrong cancellation point.
(tf): Fix check for uncontended case.
(do_test): Likewise.
* nptl/tst-cancel14.c (cleanup): Remove wrong cancellation point.
(tf): Fix check for uncontended case.
(do_test): Likewise.
* nptl/tst-cancel15.c (cleanup): Remove wrong cancellation point.
(tf): Fix check for uncontended case.
(do_test): Likewise.
107 lines
3.3 KiB
C
107 lines
3.3 KiB
C
/* sem_wait -- wait on a semaphore. Generic futex-using version.
|
|
Copyright (C) 2003-2016 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<http://www.gnu.org/licenses/>. */
|
|
|
|
#include <lowlevellock.h> /* lll_futex* used by the old code. */
|
|
#include "sem_waitcommon.c"
|
|
|
|
int
|
|
__new_sem_wait (sem_t *sem)
|
|
{
|
|
/* We need to check whether we need to act upon a cancellation request here
|
|
because POSIX specifies that cancellation points "shall occur" in
|
|
sem_wait and sem_timedwait, which also means that they need to check
|
|
this regardless whether they block or not (unlike "may occur"
|
|
functions). See the POSIX Rationale for this requirement: Section
|
|
"Thread Cancellation Overview" [1] and austin group issue #1076 [2]
|
|
for thoughs on why this may be a suboptimal design.
|
|
|
|
[1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
|
|
[2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
|
|
*/
|
|
__pthread_testcancel ();
|
|
|
|
if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
|
|
return 0;
|
|
else
|
|
return __new_sem_wait_slow((struct new_sem *) sem, NULL);
|
|
}
|
|
versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
|
|
|
|
#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
|
|
int
|
|
attribute_compat_text_section
|
|
__old_sem_wait (sem_t *sem)
|
|
{
|
|
int *futex = (int *) sem;
|
|
int err;
|
|
|
|
do
|
|
{
|
|
if (atomic_decrement_if_positive (futex) > 0)
|
|
return 0;
|
|
|
|
/* Enable asynchronous cancellation. Required by the standard. */
|
|
int oldtype = __pthread_enable_asynccancel ();
|
|
|
|
/* Always assume the semaphore is shared. */
|
|
err = lll_futex_wait (futex, 0, LLL_SHARED);
|
|
|
|
/* Disable asynchronous cancellation. */
|
|
__pthread_disable_asynccancel (oldtype);
|
|
}
|
|
while (err == 0 || err == -EWOULDBLOCK);
|
|
|
|
__set_errno (-err);
|
|
return -1;
|
|
}
|
|
|
|
compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
|
|
#endif
|
|
|
|
int
|
|
__new_sem_trywait (sem_t *sem)
|
|
{
|
|
/* We must not fail spuriously, so require a definitive result even if this
|
|
may lead to a long execution time. */
|
|
if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
|
|
return 0;
|
|
__set_errno (EAGAIN);
|
|
return -1;
|
|
}
|
|
versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
|
|
#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
|
|
int
|
|
__old_sem_trywait (sem_t *sem)
|
|
{
|
|
int *futex = (int *) sem;
|
|
int val;
|
|
|
|
if (*futex > 0)
|
|
{
|
|
val = atomic_decrement_if_positive (futex);
|
|
if (val > 0)
|
|
return 0;
|
|
}
|
|
|
|
__set_errno (EAGAIN);
|
|
return -1;
|
|
}
|
|
compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
|
|
#endif
|