ipc,shm: make shmctl_nolock lockless

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>

diff --git a/ipc/shm.c b/ipc/shm.c
index 3e123987f054b263f5f434f34de68684c6816d8c..a493639550d93111c477b66dd9315b6cc5a66b60 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;
 }