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authorDavidlohr Bueso <dave@stgolabs.net>2016-03-22 14:27:48 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-22 15:36:02 -0700
commita5f4db877177d2a3d7ae62a7bac3a5a27e083d7f (patch)
tree9cda3b63b32e98b041764acc97dd668eac070526 /ipc
parentdde5cf39d4d2cce71f2997c37210dd624d0e4bf6 (diff)
downloadlinux-a5f4db877177d2a3d7ae62a7bac3a5a27e083d7f.tar.gz
ipc/sem: make semctl setting sempid consistent
As indicated by bug#112271, Linux sets the sempid value upon semctl, and not only for semop calls. However, within semctl we only do this for SETVAL, leaving SETALL without updating the field, and therefore rather inconsistent behavior when compared to other Unices. There is really no documentation regarding this and therefore users should not make assumptions. With this patch, along with updating semctl.2 manpages, this scenario should become less ambiguous As such, set sempid on SETALL cmd. Also update some in-code documentation, specifying where the sempid is set. Passes ltp and custom testcase where a child (fork) does SETALL to the set. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Reported-by: Philip Semanchuk <linux_kernel.20.ick@spamgourmet.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com> Cc: Manfred Spraul <manfred@colorfullife.com> Cc: Herton R. Krzesinski <herton@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/sem.c13
1 files changed, 11 insertions, 2 deletions
diff --git a/ipc/sem.c b/ipc/sem.c
index cddd5b5fde51..b3757ea0694b 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -92,7 +92,14 @@
/* One semaphore structure for each semaphore in the system. */
struct sem {
int semval; /* current value */
- int sempid; /* pid of last operation */
+ /*
+ * PID of the process that last modified the semaphore. For
+ * Linux, specifically these are:
+ * - semop
+ * - semctl, via SETVAL and SETALL.
+ * - at task exit when performing undo adjustments (see exit_sem).
+ */
+ int sempid;
spinlock_t lock; /* spinlock for fine-grained semtimedop */
struct list_head pending_alter; /* pending single-sop operations */
/* that alter the semaphore */
@@ -1444,8 +1451,10 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
goto out_unlock;
}
- for (i = 0; i < nsems; i++)
+ for (i = 0; i < nsems; i++) {
sma->sem_base[i].semval = sem_io[i];
+ sma->sem_base[i].sempid = task_tgid_vnr(current);
+ }
ipc_assert_locked_object(&sma->sem_perm);
list_for_each_entry(un, &sma->list_id, list_id) {