3.16.60-rc1 review patch. If anyone has any objections, please let me know.
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From: Davidlohr Bueso dave@stgolabs.net
commit a5f4db877177d2a3d7ae62a7bac3a5a27e083d7f upstream.
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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- ipc/sem.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
--- 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 */ @@ -1469,8 +1476,10 @@ static int semctl_main(struct ipc_namesp 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) {