From 1e367efa8bd61a973bd4702de2836af8f896cb23 Mon Sep 17 00:00:00 2001 From: Jilles Tjoelker Date: Fri, 19 Apr 2013 10:16:00 +0000 Subject: [PATCH] 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 --- sys/kern/kern_umtx.c | 4 +++- sys/kern/uipc_sem.c | 2 -- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c index 6026b8080dbf..74d6d1ebb1f9 100644 --- a/sys/kern/kern_umtx.c +++ b/sys/kern/kern_umtx.c @@ -2980,7 +2980,9 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct _umtx_time *timeout) error = 0; else { umtxq_remove(uq); - if (error == ERESTART) + /* A relative timeout cannot be restarted. */ + if (error == ERESTART && timeout != NULL && + (timeout->_flags & UMTX_ABSTIME) == 0) error = EINTR; } umtxq_unlock(&uq->uq_key); diff --git a/sys/kern/uipc_sem.c b/sys/kern/uipc_sem.c index 0ea84fde44c8..509f32e909b7 100644 --- a/sys/kern/uipc_sem.c +++ b/sys/kern/uipc_sem.c @@ -846,8 +846,6 @@ kern_sem_wait(struct thread *td, semid_t id, int tryflag, err: mtx_unlock(&sem_lock); fdrop(fp, td); - if (error == ERESTART) - error = EINTR; DP(("<<< kern_sem_wait leaving, pid=%d, error = %d\n", (int)td->td_proc->p_pid, error)); return (error);