svn commit: r250569 - in stable/9: lib/libc/gen sys/kern

[Jilles Tjoelker]

Author: jilles
Date: Sun May 12 16:11:23 2013
New Revision: 250569
URL: http://svnweb.freebsd.org/changeset/base/250569

Log:
  MFC r249566,r249644: EINTR in POSIX sem_*.
  
  Document that sem_wait() can fail with [EINTR].
  
  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 old POSIX semaphore implementation did this correctly, unlike the new
  umtx one.
  
  Specific to 9-stable: UMTX_ABSTIME does not exist and therefore
  sem_timedwait() is erroneously not restarted after a SA_RESTART signal
  handler.
  
  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, as far as possible with
  the ABI in 9-stable.

Modified:
  stable/9/lib/libc/gen/sem_wait.3
  stable/9/sys/kern/kern_umtx.c
Directory Properties:
  stable/9/lib/libc/   (props changed)
  stable/9/sys/   (props changed)

Modified: stable/9/lib/libc/gen/sem_wait.3
==============================================================================
--- stable/9/lib/libc/gen/sem_wait.3	Sun May 12 16:07:23 2013	(r250568)
+++ stable/9/lib/libc/gen/sem_wait.3	Sun May 12 16:11:23 2013	(r250569)
@@ -27,7 +27,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd February 15, 2000
+.Dd April 16, 2013
 .Dt SEM_WAIT 3
 .Os
 .Sh NAME
@@ -75,6 +75,14 @@ points to an invalid semaphore.
 .El
 .Pp
 Additionally,
+.Fn sem_wait
+will fail if:
+.Bl -tag -width Er
+.Pp
+.It Bq Er EINTR
+A signal interrupted this function.
+.El
+Additionally,
 .Fn sem_trywait
 will fail if:
 .Bl -tag -width Er

Modified: stable/9/sys/kern/kern_umtx.c
==============================================================================
--- stable/9/sys/kern/kern_umtx.c	Sun May 12 16:07:23 2013	(r250568)
+++ stable/9/sys/kern/kern_umtx.c	Sun May 12 16:11:23 2013	(r250569)
@@ -2970,7 +2970,8 @@ do_sem_wait(struct thread *td, struct _u
 		error = 0;
 	else {
 		umtxq_remove(uq);
-		if (error == ERESTART)
+		/* A relative timeout cannot be restarted. */
+		if (error == ERESTART && timeout != NULL)
 			error = EINTR;
 	}
 	umtxq_unlock(&uq->uq_key);
_______________________________________________
svn-src-all at freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/svn-src-all
To unsubscribe, send any mail to "svn-src-all-unsubscribe at freebsd.org"