ceph: try to queue a writeback if revoking fails

If the pagecaches writeback just finished and the i_wrbuffer_ref
reaches zero it will try to trigger ceph_check_caps(). But if just
before ceph_check_caps() the i_wrbuffer_ref could be increased
again by mmap/cache write, then the Fwb revoke will fail.

We need to try to queue a writeback in this case instead of
triggering the writeback by BDI's delayed work per 5 seconds.

URL: https://tracker.ceph.com/issues/46904
URL: https://tracker.ceph.com/issues/55377
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index a051e6e..bf2e940 100644 (file)
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1911,6 +1911,7 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
        struct rb_node *p;
        bool queue_invalidate = false;
        bool tried_invalidate = false;
+       bool queue_writeback = false;
 
        if (session)
                ceph_get_mds_session(session);
@@ -2063,10 +2064,27 @@ retry:
                }
 
                /* completed revocation? going down and there are no caps? */
-               if (revoking && (revoking & cap_used) == 0) {
-                       dout("completed revocation of %s\n",
-                            ceph_cap_string(cap->implemented & ~cap->issued));
-                       goto ack;
+               if (revoking) {
+                       if ((revoking & cap_used) == 0) {
+                               dout("completed revocation of %s\n",
+                                     ceph_cap_string(cap->implemented & ~cap->issued));
+                               goto ack;
+                       }
+
+                       /*
+                        * If the "i_wrbuffer_ref" was increased by mmap or generic
+                        * cache write just before the ceph_check_caps() is called,
+                        * the Fb capability revoking will fail this time. Then we
+                        * must wait for the BDI's delayed work to flush the dirty
+                        * pages and to release the "i_wrbuffer_ref", which will cost
+                        * at most 5 seconds. That means the MDS needs to wait at
+                        * most 5 seconds to finished the Fb capability's revocation.
+                        *
+                        * Let's queue a writeback for it.
+                        */
+                       if (S_ISREG(inode->i_mode) && ci->i_wrbuffer_ref &&
+                           (revoking & CEPH_CAP_FILE_BUFFER))
+                               queue_writeback = true;
                }
 
                /* want more caps from mds? */
@@ -2136,6 +2154,8 @@ ack:
        spin_unlock(&ci->i_ceph_lock);
 
        ceph_put_mds_session(session);
+       if (queue_writeback)
+               ceph_queue_writeback(inode);
        if (queue_invalidate)
                ceph_queue_invalidate(inode);
 }