ipc/sem.c: synchronize the proc interface

The proc interface is not aware of sem_lock(), it instead calls
ipc_lock_object() directly.  This means that simple semop() operations
can run in parallel with the proc interface.  Right now, this is
uncritical, because the implementation doesn't do anything that requires
a proper synchronization.

But it is dangerous and therefore should be fixed.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index e20658d76bb5..cd6a733011a2 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2103,6 +2103,14 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
         struct sem_array *sma = it;
         time_t sem_otime;
 
+        /*
+         * The proc interface isn't aware of sem_lock(), it calls
+         * ipc_lock_object() directly (in sysvipc_find_ipc).
+         * In order to stay compatible with sem_lock(), we must wait until
+         * all simple semop() calls have left their critical regions.
+         */
+        sem_wait_array(sma);
+
         sem_otime = get_semotime(sma);
 
         return seq_printf(s,