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Subject[ 38/69] ipc,msg: shorten critical region in msgsnd
Date
3.10-stable review patch.  If anyone has any objections, please let me know.

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

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

commit 3dd1f784ed6603d7ab1043e51e6371235edf2313 upstream.

do_msgsnd() is another function that does too many things with the ipc
object lock acquired. Take it only when needed when actually updating
msq.

Signed-off-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Andi Kleen <andi@firstfloor.org>
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>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
ipc/msg.c | 37 ++++++++++++++++++++++++-------------
1 file changed, 24 insertions(+), 13 deletions(-)

--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -698,10 +698,11 @@ long do_msgsnd(int msqid, long mtype, vo
msg->m_type = mtype;
msg->m_ts = msgsz;

- msq = msg_lock_check(ns, msqid);
+ rcu_read_lock();
+ msq = msq_obtain_object_check(ns, msqid);
if (IS_ERR(msq)) {
err = PTR_ERR(msq);
- goto out_free;
+ goto out_unlock1;
}

for (;;) {
@@ -709,11 +710,11 @@ long do_msgsnd(int msqid, long mtype, vo

err = -EACCES;
if (ipcperms(ns, &msq->q_perm, S_IWUGO))
- goto out_unlock_free;
+ goto out_unlock1;

err = security_msg_queue_msgsnd(msq, msg, msgflg);
if (err)
- goto out_unlock_free;
+ goto out_unlock1;

if (msgsz + msq->q_cbytes <= msq->q_qbytes &&
1 + msq->q_qnum <= msq->q_qbytes) {
@@ -723,32 +724,41 @@ long do_msgsnd(int msqid, long mtype, vo
/* queue full, wait: */
if (msgflg & IPC_NOWAIT) {
err = -EAGAIN;
- goto out_unlock_free;
+ goto out_unlock1;
}
+
+ ipc_lock_object(&msq->q_perm);
ss_add(msq, &s);

if (!ipc_rcu_getref(msq)) {
err = -EIDRM;
- goto out_unlock_free;
+ goto out_unlock0;
}

- msg_unlock(msq);
+ ipc_unlock_object(&msq->q_perm);
+ rcu_read_unlock();
schedule();

- ipc_lock_by_ptr(&msq->q_perm);
+ rcu_read_lock();
+ ipc_lock_object(&msq->q_perm);
+
ipc_rcu_putref(msq);
if (msq->q_perm.deleted) {
err = -EIDRM;
- goto out_unlock_free;
+ goto out_unlock0;
}
+
ss_del(&s);

if (signal_pending(current)) {
err = -ERESTARTNOHAND;
- goto out_unlock_free;
+ goto out_unlock0;
}
+
+ ipc_unlock_object(&msq->q_perm);
}

+ ipc_lock_object(&msq->q_perm);
msq->q_lspid = task_tgid_vnr(current);
msq->q_stime = get_seconds();

@@ -764,9 +774,10 @@ long do_msgsnd(int msqid, long mtype, vo
err = 0;
msg = NULL;

-out_unlock_free:
- msg_unlock(msq);
-out_free:
+out_unlock0:
+ ipc_unlock_object(&msq->q_perm);
+out_unlock1:
+ rcu_read_unlock();
if (msg != NULL)
free_msg(msg);
return err;



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