From: Davidlohr Bueso <davidlohr.bueso@hp.com>
Date: Wed, 11 Sep 2013 21:26:20 +0000 (-0700)
Subject: ipc,shm: make shmctl_nolock lockless
X-Git-Tag: firefly_0821_release~6453^2~487
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=c29c40392a01b9414b02c1b57b042950704cb774;p=firefly-linux-kernel-4.4.55.git

ipc,shm: make shmctl_nolock lockless

commit c97cb9ccab8c85428ec21eff690642ad2ce1fa8a upstream.

While the INFO cmd doesn't take the ipc lock, the STAT commands do acquire
it unnecessarily.  We can do the permissions and security checks only
holding the rcu lock.

[akpm@linux-foundation.org: coding-style fixes]
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>
---

diff --git a/ipc/shm.c b/ipc/shm.c
index ac118becb83a..8fd9ab38e766 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -882,27 +882,31 @@ static int shmctl_nolock(struct ipc_namespace *ns, int shmid,
 		struct shmid64_ds tbuf;
 		int result;
 
+		rcu_read_lock();
 		if (cmd == SHM_STAT) {
-			shp = shm_lock(ns, shmid);
+			shp = shm_obtain_object(ns, shmid);
 			if (IS_ERR(shp)) {
 				err = PTR_ERR(shp);
-				goto out;
+				goto out_unlock;
 			}
 			result = shp->shm_perm.id;
 		} else {
-			shp = shm_lock_check(ns, shmid);
+			shp = shm_obtain_object_check(ns, shmid);
 			if (IS_ERR(shp)) {
 				err = PTR_ERR(shp);
-				goto out;
+				goto out_unlock;
 			}
 			result = 0;
 		}
+
 		err = -EACCES;
 		if (ipcperms(ns, &shp->shm_perm, S_IRUGO))
 			goto out_unlock;
+
 		err = security_shm_shmctl(shp, cmd);
 		if (err)
 			goto out_unlock;
+
 		memset(&tbuf, 0, sizeof(tbuf));
 		kernel_to_ipc64_perm(&shp->shm_perm, &tbuf.shm_perm);
 		tbuf.shm_segsz	= shp->shm_segsz;
@@ -912,8 +916,9 @@ static int shmctl_nolock(struct ipc_namespace *ns, int shmid,
 		tbuf.shm_cpid	= shp->shm_cprid;
 		tbuf.shm_lpid	= shp->shm_lprid;
 		tbuf.shm_nattch	= shp->shm_nattch;
-		shm_unlock(shp);
-		if(copy_shmid_to_user (buf, &tbuf, version))
+		rcu_read_unlock();
+
+		if (copy_shmid_to_user(buf, &tbuf, version))
 			err = -EFAULT;
 		else
 			err = result;
@@ -924,7 +929,7 @@ static int shmctl_nolock(struct ipc_namespace *ns, int shmid,
 	}
 
 out_unlock:
-	shm_unlock(shp);
+	rcu_read_unlock();
 out:
 	return err;
 }