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Subject[ 49/69] ipc,shm: shorten critical region in shmctl_down
Date
3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Davidlohr Bueso <davidlohr.bueso@hp.com>

commit 79ccf0f8c8e04e8b9eda6645ba0f63b0915a3075 upstream.

Instead of holding the ipc lock for the entire function, use the
ipcctl_pre_down_nolock and only acquire the lock for specific commands:
RMID and SET.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
ipc/shm.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -780,11 +780,10 @@ static int shmctl_down(struct ipc_namesp
down_write(&shm_ids(ns).rw_mutex);
rcu_read_lock();

- ipcp = ipcctl_pre_down(ns, &shm_ids(ns), shmid, cmd,
- &shmid64.shm_perm, 0);
+ ipcp = ipcctl_pre_down_nolock(ns, &shm_ids(ns), shmid, cmd,
+ &shmid64.shm_perm, 0);
if (IS_ERR(ipcp)) {
err = PTR_ERR(ipcp);
- /* the ipc lock is not held upon failure */
goto out_unlock1;
}

@@ -792,14 +791,16 @@ static int shmctl_down(struct ipc_namesp

err = security_shm_shmctl(shp, cmd);
if (err)
- goto out_unlock0;
+ goto out_unlock1;

switch (cmd) {
case IPC_RMID:
+ ipc_lock_object(&shp->shm_perm);
/* do_shm_rmid unlocks the ipc object and rcu */
do_shm_rmid(ns, ipcp);
goto out_up;
case IPC_SET:
+ ipc_lock_object(&shp->shm_perm);
err = ipc_update_perm(&shmid64.shm_perm, ipcp);
if (err)
goto out_unlock0;
@@ -807,6 +808,7 @@ static int shmctl_down(struct ipc_namesp
break;
default:
err = -EINVAL;
+ goto out_unlock1;
}

out_unlock0:



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