The patch titled
Subject: ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()
has been added to the -mm tree. Its filename is
ipcsem-remove-uneeded-sem_undo_list-lock-usage-in-exit_sem.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/ipcsem-remove-uneeded-sem_undo_list-lock-usage-in-exit_sem.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/ipcsem-remove-uneeded-sem_undo_list-lock-usage-in-exit_sem.patch
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------------------------------------------------------
From: "Herton R. Krzesinski" <herton@xxxxxxxxxx>
Subject: ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()
After we acquire the sma->sem_perm lock in exit_sem(), we are protected
against a racing IPC_RMID operation. Also at that point, we are the last
user of sem_undo_list. Therefore it isn't required that we acquire or use
ulp->lock.
Signed-off-by: Herton R. Krzesinski <herton@xxxxxxxxxx>
Acked-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
CC: Aristeu Rozanski <aris@xxxxxxxxxx>
Cc: David Jeffery <djeffery@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
ipc/sem.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN ipc/sem.c~ipcsem-remove-uneeded-sem_undo_list-lock-usage-in-exit_sem ipc/sem.c
--- a/ipc/sem.c~ipcsem-remove-uneeded-sem_undo_list-lock-usage-in-exit_sem
+++ a/ipc/sem.c
@@ -2123,9 +2123,11 @@ void exit_sem(struct task_struct *tsk)
ipc_assert_locked_object(&sma->sem_perm);
list_del(&un->list_id);
- spin_lock(&ulp->lock);
+ /* we are the last process using this ulp, acquiring ulp->lock
+ * isn't required. Besides that, we are also protected against
+ * IPC_RMID as we hold sma->sem_perm lock now
+ */
list_del_rcu(&un->list_proc);
- spin_unlock(&ulp->lock);
/* perform adjustments registered in un */
for (i = 0; i < sma->sem_nsems; i++) {
_
Patches currently in -mm which might be from herton@xxxxxxxxxx are
ipcsem-fix-use-after-free-on-ipc_rmid-after-a-task-using-same-semaphore-set-exits.patch
ipcsem-fix-use-after-free-on-ipc_rmid-after-a-task-using-same-semaphore-set-exits-fix.patch
ipcsem-remove-uneeded-sem_undo_list-lock-usage-in-exit_sem.patch
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