ceph: take i_mutex before getting Fw cap

There is deadlock as illustrated bellow. The fix is taking i_mutex
before getting Fw cap reference.

      write                    truncate                 MDS
---------------------     --------------------      --------------
get Fw cap
                          lock i_mutex
lock i_mutex (blocked)
                          request setattr.size  ->
                                                <-   revoke Fw cap

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Reviewed-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

1 files changed, 7 insertions, 6 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index f9563108d189..da0f9b8a3bcb 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2052,6 +2052,13 @@ static int try_get_cap_refs(struct ceph_inode_info *ci, int need, int want,
                 goto out;
         }
 
+        /* finish pending truncate */
+        while (ci->i_truncate_pending) {
+                spin_unlock(&ci->i_ceph_lock);
+                __ceph_do_pending_vmtruncate(inode, !(need & CEPH_CAP_FILE_WR));
+                spin_lock(&ci->i_ceph_lock);
+        }
+
         if (need & CEPH_CAP_FILE_WR) {
                 if (endoff >= 0 && endoff > (loff_t)ci->i_max_size) {
                         dout("get_cap_refs %p endoff %llu > maxsize %llu\n",
@@ -2073,12 +2080,6 @@ static int try_get_cap_refs(struct ceph_inode_info *ci, int need, int want,
         }
         have = __ceph_caps_issued(ci, &implemented);
 
-        /*
-         * disallow writes while a truncate is pending
-         */
-        if (ci->i_truncate_pending)
-                have &= ~CEPH_CAP_FILE_WR;
-
         if ((have & need) == need) {
                 /*
                  * Look at (implemented & ~have & not) so that we keep waiting