ceph: fix session locking in handle_caps, ceph_check_caps

Passing a session pointer to ceph_check_caps() used to mean it would leave
the session mutex locked.  That wasn't always possible if it wasn't passed
CHECK_CAPS_AUTHONLY.   If could unlock the passed session and lock a
differet session mutex, which was clearly wrong, and also emitted a
warning when it a racing CPU retook it and we did an unlock from the wrong
context.

This was only a problem when there was more than one MDS.

First, make ceph_check_caps unconditionally drop the session mutex, so that
it is free to lock other sessions as needed.  Then adjust the one caller
that passes in a session (handle_cap_grant) accordingly.

Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 726c8d445995fd5d7feea276b595779871823c22..782848632e81f14ebce5c816464393ea8890d764 100644 (file)
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1407,6 +1407,7 @@ static int try_nonblocking_invalidate(struct inode *inode)
  */
 void ceph_check_caps(struct ceph_inode_info *ci, int flags,
                     struct ceph_mds_session *session)
+       __releases(session->s_mutex)
 {
        struct ceph_client *client = ceph_inode_to_client(&ci->vfs_inode);
        struct ceph_mds_client *mdsc = &client->mdsc;
@@ -1414,7 +1415,6 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
        struct ceph_cap *cap;
        int file_wanted, used;
        int took_snap_rwsem = 0;             /* true if mdsc->snap_rwsem held */
-       int drop_session_lock = session ? 0 : 1;
        int issued, implemented, want, retain, revoking, flushing = 0;
        int mds = -1;   /* keep track of how far we've gone through i_caps list
                           to avoid an infinite loop on retry */
@@ -1639,7 +1639,7 @@ ack:
        if (queue_invalidate)
                ceph_queue_invalidate(inode);
 
-       if (session && drop_session_lock)
+       if (session)
                mutex_unlock(&session->s_mutex);
        if (took_snap_rwsem)
                up_read(&mdsc->snap_rwsem);
@@ -2688,14 +2688,17 @@ void ceph_handle_caps(struct ceph_mds_session *session,
        case CEPH_CAP_OP_REVOKE:
        case CEPH_CAP_OP_GRANT:
                r = handle_cap_grant(inode, h, session, cap, msg->middle);
-               if (r == 1)
+               if (r == 1) {
                        ceph_check_caps(ceph_inode(inode),
                                        CHECK_CAPS_NODELAY|CHECK_CAPS_AUTHONLY,
                                        session);
-               else if (r == 2)
+                       session = NULL;
+               } else if (r == 2) {
                        ceph_check_caps(ceph_inode(inode),
                                        CHECK_CAPS_NODELAY,
                                        session);
+                       session = NULL;
+               }
                break;
 
        case CEPH_CAP_OP_FLUSH_ACK:
@@ -2713,7 +2716,8 @@ void ceph_handle_caps(struct ceph_mds_session *session,
        }
 
 done:
-       mutex_unlock(&session->s_mutex);
+       if (session)
+               mutex_unlock(&session->s_mutex);
 
        if (check_caps)
                ceph_check_caps(ceph_inode(inode), CHECK_CAPS_NODELAY, NULL);