[PATCH] ipc/sem.c: Synchronize the proc interface

[Manfred Spraul]

The proc interface is not aware of sem_lock(), it 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.

Andrew:
- Could you include the patch in -mm and push it towards Linus?
- The patch depends on ipc-semc-fix-race-in-sem_lock.patch

Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
---
 ipc/sem.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/ipc/sem.c b/ipc/sem.c
index 4a92c04..e5d9bb8 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2095,6 +2095,14 @@ 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,
-- 
1.8.3.1

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