d/freebsd-skq
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

sem: Restart the POSIX sem_* calls after signals with SA_RESTART set.

Browse Source 
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:
Jilles Tjoelker 2013-04-19 10:16:00 +00:00
parent 7904f51655
commit 1e367efa8b
2 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
sys/kern/kern_umtx.c
View File

@ -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);

2
sys/kern/uipc_sem.c
View File

@ -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);