ceph: don't take s_mutex or snap_rwsem in ceph_check_caps

These locks appear to be completely unnecessary. Almost all of this
function is done under the inode->i_ceph_lock, aside from the actual
sending of the message. Don't take either lock in this function.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Luis Henriques <lhenriques@suse.de>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: jtlayton

fs/ceph/caps.c

@@ -1912,22 +1912,20 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 	struct ceph_cap *cap;
 	u64 flush_tid, oldest_flush_tid;
 	int file_wanted, used, cap_used;
-	int took_snap_rwsem = 0;             /* true if mdsc->snap_rwsem held */
 	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 */
 	struct rb_node *p;
 	bool queue_invalidate = false;
 	bool tried_invalidate = false;
 
+	if (session)
+		ceph_get_mds_session(session);
+
 	spin_lock(&ci->i_ceph_lock);
 	if (ci->i_ceph_flags & CEPH_I_FLUSH)
 		flags |= CHECK_CAPS_FLUSH;
-
-	goto retry_locked;
 retry:
-	spin_lock(&ci->i_ceph_lock);
-retry_locked:
 	/* Caps wanted by virtue of active open files. */
 	file_wanted = __ceph_caps_file_wanted(ci);
 
@@ -2007,7 +2005,7 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 			ci->i_rdcache_revoking = ci->i_rdcache_gen;
 		}
 		tried_invalidate = true;
-		goto retry_locked;
+		goto retry;
 	}
 
 	for (p = rb_first(&ci->i_caps); p; p = rb_next(p)) {
@@ -2021,8 +2019,6 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 		    ((flags & CHECK_CAPS_AUTHONLY) && cap != ci->i_auth_cap))
 			continue;
 
-		/* NOTE: no side-effects allowed, until we take s_mutex */
-
 		/*
 		 * If we have an auth cap, we don't need to consider any
 		 * overlapping caps as used.
@@ -2085,37 +2081,8 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 			continue;     /* nope, all good */
 
 ack:
-		if (session && session != cap->session) {
-			dout("oops, wrong session %p mutex\n", session);
-			mutex_unlock(&session->s_mutex);
-			session = NULL;
-		}
-		if (!session) {
-			session = cap->session;
-			if (mutex_trylock(&session->s_mutex) == 0) {
-				dout("inverting session/ino locks on %p\n",
-				     session);
-				session = ceph_get_mds_session(session);
-				spin_unlock(&ci->i_ceph_lock);
-				if (took_snap_rwsem) {
-					up_read(&mdsc->snap_rwsem);
-					took_snap_rwsem = 0;
-				}
-				if (session) {
-					mutex_lock(&session->s_mutex);
-					ceph_put_mds_session(session);
-				} else {
-					/*
-					 * Because we take the reference while
-					 * holding the i_ceph_lock, it should
-					 * never be NULL. Throw a warning if it
-					 * ever is.
-					 */
-					WARN_ON_ONCE(true);
-				}
-				goto retry;
-			}
-		}
+		ceph_put_mds_session(session);
+		session = ceph_get_mds_session(cap->session);
 
 		/* kick flushing and flush snaps before sending normal
 		 * cap message */
@@ -2127,20 +2094,7 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 			if (ci->i_ceph_flags & CEPH_I_FLUSH_SNAPS)
 				__ceph_flush_snaps(ci, session);
 
-			goto retry_locked;
-		}
-
-		/* take snap_rwsem after session mutex */
-		if (!took_snap_rwsem) {
-			if (down_read_trylock(&mdsc->snap_rwsem) == 0) {
-				dout("inverting snap/in locks on %p\n",
-				     inode);
-				spin_unlock(&ci->i_ceph_lock);
-				down_read(&mdsc->snap_rwsem);
-				took_snap_rwsem = 1;
-				goto retry;
-			}
-			took_snap_rwsem = 1;
+			goto retry;
 		}
 
 		if (cap == ci->i_auth_cap && ci->i_dirty_caps) {
@@ -2162,9 +2116,10 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 
 		__prep_cap(&arg, cap, CEPH_CAP_OP_UPDATE, mflags, cap_used,
 			   want, retain, flushing, flush_tid, oldest_flush_tid);
-		spin_unlock(&ci->i_ceph_lock);
 
+		spin_unlock(&ci->i_ceph_lock);
 		__send_cap(&arg, ci);
+		spin_lock(&ci->i_ceph_lock);
 
 		goto retry; /* retake i_ceph_lock and restart our cap scan. */
 	}
@@ -2179,13 +2134,9 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 
 	spin_unlock(&ci->i_ceph_lock);
 
+	ceph_put_mds_session(session);
 	if (queue_invalidate)
 		ceph_queue_invalidate(inode);
-
-	if (session)
-		mutex_unlock(&session->s_mutex);
-	if (took_snap_rwsem)
-		up_read(&mdsc->snap_rwsem);
 }
 
 /*
@@ -3550,13 +3501,12 @@ static void handle_cap_grant(struct inode *inode,
 	if (wake)
 		wake_up_all(&ci->i_cap_wq);
 
+	mutex_unlock(&session->s_mutex);
 	if (check_caps == 1)
 		ceph_check_caps(ci, CHECK_CAPS_AUTHONLY | CHECK_CAPS_NOINVAL,
 				session);
 	else if (check_caps == 2)
 		ceph_check_caps(ci, CHECK_CAPS_NOINVAL, session);
-	else
-		mutex_unlock(&session->s_mutex);
 }
 
 /*