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290db09546
Some Linux interfaces never restart after being interrupted by a signal handler, regardless of the use of SA_RESTART [1]. It means that for pthread cancellation, if the target thread disables cancellation with pthread_setcancelstate and calls such interfaces (like poll or select), it should not see spurious EINTR failures due the internal SIGCANCEL. However recent changes made pthread_cancel to always sent the internal signal, regardless of the target thread cancellation status or type. To fix it, the previous semantic is restored, where the cancel signal is only sent if the target thread has cancelation enabled in asynchronous mode. The cancel state and cancel type is moved back to cancelhandling and atomic operation are used to synchronize between threads. The patch essentially revert the following commits:8c1c0aae20
nptl: Move cancel type out of cancelhandling2b51742531
nptl: Move cancel state out of cancelhandling26cfbb7162
nptl: Remove CANCELING_BITMASK However I changed the atomic operation to follow the internal C11 semantic and removed the MACRO usage, it simplifies a bit the resulting code (and removes another usage of the old atomic macros). Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu, and powerpc64-linux-gnu. [1] https://man7.org/linux/man-pages/man7/signal.7.html Reviewed-by: Florian Weimer <fweimer@redhat.com> Tested-by: Aurelien Jarno <aurelien@aurel32.net> (cherry-picked from commit404656009b
)
134 lines
4.6 KiB
C
134 lines
4.6 KiB
C
/* Common definition for pthread_{timed,try}join{_np}.
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Copyright (C) 2017-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include "pthreadP.h"
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#include <atomic.h>
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#include <stap-probe.h>
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#include <time.h>
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#include <futex-internal.h>
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static void
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cleanup (void *arg)
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{
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/* If we already changed the waiter ID, reset it. The call cannot
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fail for any reason but the thread not having done that yet so
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there is no reason for a loop. */
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struct pthread *self = THREAD_SELF;
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atomic_compare_exchange_weak_acquire (&arg, &self, NULL);
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}
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int
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__pthread_clockjoin_ex (pthread_t threadid, void **thread_return,
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clockid_t clockid,
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const struct __timespec64 *abstime, bool block)
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{
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struct pthread *pd = (struct pthread *) threadid;
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/* Make sure the descriptor is valid. */
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if (INVALID_NOT_TERMINATED_TD_P (pd))
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/* Not a valid thread handle. */
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return ESRCH;
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/* Is the thread joinable?. */
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if (IS_DETACHED (pd))
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/* We cannot wait for the thread. */
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return EINVAL;
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struct pthread *self = THREAD_SELF;
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int result = 0;
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LIBC_PROBE (pthread_join, 1, threadid);
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if ((pd == self
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|| (self->joinid == pd
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&& (pd->cancelhandling
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& (CANCELING_BITMASK | CANCELED_BITMASK | EXITING_BITMASK
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| TERMINATED_BITMASK)) == 0))
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&& !cancel_enabled_and_canceled (self->cancelhandling))
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/* This is a deadlock situation. The threads are waiting for each
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other to finish. Note that this is a "may" error. To be 100%
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sure we catch this error we would have to lock the data
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structures but it is not necessary. In the unlikely case that
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two threads are really caught in this situation they will
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deadlock. It is the programmer's problem to figure this
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out. */
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return EDEADLK;
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/* Wait for the thread to finish. If it is already locked something
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is wrong. There can only be one waiter. */
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else if (__glibc_unlikely (atomic_compare_exchange_weak_acquire (&pd->joinid,
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&self,
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NULL)))
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/* There is already somebody waiting for the thread. */
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return EINVAL;
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/* BLOCK waits either indefinitely or based on an absolute time. POSIX also
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states a cancellation point shall occur for pthread_join, and we use the
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same rationale for posix_timedjoin_np. Both clockwait_tid and the futex
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call use the cancellable variant. */
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if (block)
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{
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/* During the wait we change to asynchronous cancellation. If we
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are cancelled the thread we are waiting for must be marked as
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un-wait-ed for again. */
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pthread_cleanup_push (cleanup, &pd->joinid);
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/* We need acquire MO here so that we synchronize with the
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kernel's store to 0 when the clone terminates. (see above) */
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pid_t tid;
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while ((tid = atomic_load_acquire (&pd->tid)) != 0)
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{
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/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via
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futex wake-up when the clone terminates. The memory location
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contains the thread ID while the clone is running and is reset to
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zero by the kernel afterwards. The kernel up to version 3.16.3
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does not use the private futex operations for futex wake-up when
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the clone terminates. */
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int ret = __futex_abstimed_wait_cancelable64 (
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(unsigned int *) &pd->tid, tid, clockid, abstime, LLL_SHARED);
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if (ret == ETIMEDOUT || ret == EOVERFLOW)
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{
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result = ret;
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break;
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}
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}
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pthread_cleanup_pop (0);
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}
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void *pd_result = pd->result;
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if (__glibc_likely (result == 0))
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{
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/* We mark the thread as terminated and as joined. */
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pd->tid = -1;
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/* Store the return value if the caller is interested. */
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if (thread_return != NULL)
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*thread_return = pd_result;
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/* Free the TCB. */
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__nptl_free_tcb (pd);
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}
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else
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pd->joinid = NULL;
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LIBC_PROBE (pthread_join_ret, 3, threadid, result, pd_result);
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return result;
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}
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