Date: Sun, 4 May 2014 12:40:01 GMT From: Konstantin Belousov <kostikbel@gmail.com> To: freebsd-standards@FreeBSD.org Subject: Re: standards/189353: POSIX sem_unlink does not actually unlink the semaphore in the process context Message-ID: <201405041240.s44Ce0he077506@freefall.freebsd.org>
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The following reply was made to PR standards/189353; it has been noted by GNATS.
From: Konstantin Belousov <kostikbel@gmail.com>
To: Joris <joris@giovannangeli.fr>
Cc: freebsd-gnats-submit@FreeBSD.org
Subject: Re: standards/189353: POSIX sem_unlink does not actually unlink the
semaphore in the process context
Date: Sun, 4 May 2014 15:37:43 +0300
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On Sun, May 04, 2014 at 11:15:23AM +0000, Joris wrote:
>=20
> >Number: 189353
> >Category: standards
> >Synopsis: POSIX sem_unlink does not actually unlink the semaphore =
in the process context
> >Confidential: no
> >Severity: non-critical
> >Priority: low
> >Responsible: freebsd-standards
> >State: open
> >Quarter: =20
> >Keywords: =20
> >Date-Required:
> >Class: sw-bug
> >Submitter-Id: current-users
> >Arrival-Date: Sun May 04 11:20:00 UTC 2014
> >Closed-Date:
> >Last-Modified:
> >Originator: Joris
> >Release: freebsd 10
> >Organization:
> >Environment:
> >Description:
> When a posix sempahore is open, it is cached in the process address space=
=2E A call to sem_unlink does not invalidate the caching, and trying to reo=
pen the semaphore with O_EXCL after calling sem_unlink fails with EEXIST.
> >How-To-Repeat:
> Here is a test case :
>=20
> #include <fcntl.h>
> #include <sys/stat.h>
> #include <sys/wait.h>
> #include <sys/types.h>
> #include <semaphore.h>
>=20
> #include <err.h>
>=20
>=20
> int
> main(int argc, char *argv[])
> {
> sem_t *sem1, *sem2;
> int error;
>=20
> sem1 =3D sem_open("/test-sem1", O_CREAT | O_EXCL, S_IRWXU, 1);
> if (sem1 =3D=3D SEM_FAILED)
> err(1,"Cannot create test /test-sem1 semaphore");
>=20
> error =3D sem_unlink("/test-sem1");
>=20
> if (error)
> err(1, "Cannot unlink semaphore /test-sem1");
>=20
>=20
> sem2 =3D sem_open("/test-sem1", O_CREAT | O_EXCL, S_IRWXU, 2);
>=20
> if (sem2 =3D=3D SEM_FAILED)
> err(1, "Cannot re-create semaphore /test-sem1");
>=20
> error =3D sem_unlink("/test-sem1");
>=20
> if (error)
> err(1, "Cannot unlink semaphore /test-sem1");
>=20
> return(0);
> }
Yes, I think you are right. Please try the following patch, which worked
for me, but I only lightly tested it.
diff --git a/lib/libc/gen/sem_new.c b/lib/libc/gen/sem_new.c
index 9a2ab27..8e4a91d 100644
--- a/lib/libc/gen/sem_new.c
+++ b/lib/libc/gen/sem_new.c
@@ -161,7 +161,7 @@ _sem_open(const char *name, int flags, ...)
=20
_pthread_mutex_lock(&sem_llock);
LIST_FOREACH(ni, &sem_list, next) {
- if (strcmp(name, ni->name) =3D=3D 0) {
+ if (ni->name !=3D NULL && strcmp(name, ni->name) =3D=3D 0) {
if ((flags & (O_CREAT|O_EXCL)) =3D=3D (O_CREAT|O_EXCL)) {
_pthread_mutex_unlock(&sem_llock);
errno =3D EEXIST;
@@ -287,20 +287,32 @@ _sem_close(sem_t *sem)
int
_sem_unlink(const char *name)
{
+ struct sem_nameinfo *ni;
char path[PATH_MAX];
+ int error;
=20
if (name[0] !=3D '/') {
errno =3D ENOENT;
return -1;
}
name++;
-
strcpy(path, SEM_PREFIX);
if (strlcat(path, name, sizeof(path)) >=3D sizeof(path)) {
errno =3D ENAMETOOLONG;
return (-1);
}
- return unlink(path);
+
+ _pthread_once(&once, sem_module_init);
+ _pthread_mutex_lock(&sem_llock);
+ LIST_FOREACH(ni, &sem_list, next) {
+ if (ni->name !=3D NULL && strcmp(name, ni->name) =3D=3D 0) {
+ ni->name =3D NULL;
+ break;
+ }
+ }
+ error =3D unlink(path);
+ _pthread_mutex_unlock(&sem_llock);
+ return (error);
}
=20
int
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