commit 604d1b0245b97738cde4341944ad93edff4b2827
author Yan, Zheng <zyan@redhat.com> Fri May 01 17:49:16 2015 +0800
committer Ilya Dryomov <idryomov@gmail.com> Thu Jun 25 11:49:28 2015 +0300
tree 05a75dfc1ddf4729405f9cb6ce2f405b8e47791e
parent 860560904962d08fd38666207c910065fe53e074

ceph: take snap_rwsem when accessing snap realm's cached_context

When ceph inode's i_head_snapc is NULL, __ceph_mark_dirty_caps()
accesses snap realm's cached_context. So we need take read lock
of snap_rwsem.

Signed-off-by: Yan, Zheng <zyan@redhat.com>

fs/ceph/inode.c

diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 1a68c0e..1c991df 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -1727,6 +1727,7 @@
 	int mask = 0;
 	int err = 0;
 	int inode_dirty_flags = 0;
+	bool lock_snap_rwsem = false;
 
 	if (ceph_snap(inode) != CEPH_NOSNAP)
 		return -EROFS;
@@ -1742,6 +1743,18 @@
 
 	spin_lock(&ci->i_ceph_lock);
 	issued = __ceph_caps_issued(ci, NULL);
+
+	if (!ci->i_head_snapc &&
+	    (issued & (CEPH_CAP_ANY_EXCL | CEPH_CAP_FILE_WR))) {
+		lock_snap_rwsem = true;
+		if (!down_read_trylock(&mdsc->snap_rwsem)) {
+			spin_unlock(&ci->i_ceph_lock);
+			down_read(&mdsc->snap_rwsem);
+			spin_lock(&ci->i_ceph_lock);
+			issued = __ceph_caps_issued(ci, NULL);
+		}
+	}
+
 	dout("setattr %p issued %s\n", inode, ceph_cap_string(issued));
 
 	if (ia_valid & ATTR_UID) {
@@ -1890,6 +1903,8 @@
 
 	release &= issued;
 	spin_unlock(&ci->i_ceph_lock);
+	if (lock_snap_rwsem)
+		up_read(&mdsc->snap_rwsem);
 
 	if (inode_dirty_flags)
 		__mark_inode_dirty(inode, inode_dirty_flags);