sem: Restart the POSIX sem_* calls after signals with SA_RESTART set.
Programs often do not expect an [EINTR] return from sem_wait() and POSIX only allows it if the signal was installed without SA_RESTART. The timeout in sem_timedwait() is absolute so it can be restarted normally. The umtx call can be invoked with a relative timeout and in that case [ERESTART] must be changed to [EINTR]. However, libc does not do this. The old POSIX semaphore implementation did this correctly (before r249566), unlike the new umtx one. It may be desirable to avoid [EINTR] completely, which matches the pthread functions and is explicitly permitted by POSIX. However, the kernel must return [EINTR] at least for signals with SA_RESTART clear, otherwise pthread cancellation will not abort a semaphore wait. In this commit, only restore the 8.x behaviour which is also permitted by POSIX. Discussed with: jhb MFC after: 1 week
This commit is contained in:
parent
7904f51655
commit
1e367efa8b
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=249644
@ -2980,7 +2980,9 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct _umtx_time *timeout)
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error = 0;
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error = 0;
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else {
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else {
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umtxq_remove(uq);
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umtxq_remove(uq);
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if (error == ERESTART)
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/* A relative timeout cannot be restarted. */
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if (error == ERESTART && timeout != NULL &&
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(timeout->_flags & UMTX_ABSTIME) == 0)
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error = EINTR;
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error = EINTR;
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}
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}
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umtxq_unlock(&uq->uq_key);
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umtxq_unlock(&uq->uq_key);
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@ -846,8 +846,6 @@ kern_sem_wait(struct thread *td, semid_t id, int tryflag,
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err:
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err:
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mtx_unlock(&sem_lock);
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mtx_unlock(&sem_lock);
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fdrop(fp, td);
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fdrop(fp, td);
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if (error == ERESTART)
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error = EINTR;
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DP(("<<< kern_sem_wait leaving, pid=%d, error = %d\n",
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DP(("<<< kern_sem_wait leaving, pid=%d, error = %d\n",
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(int)td->td_proc->p_pid, error));
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(int)td->td_proc->p_pid, error));
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return (error);
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return (error);
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