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 ac118becb83ab55c60ea644776f4ab0f64483438..8fd9ab38e7667562e0cc8d65118f03f2779fa767 100644 (file)
--- 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;
 }