ceph: defer flushing the capsnap if the Fb is used

If the Fb cap is used it means the current inode is flushing the
dirty data to OSD, just defer flushing the capsnap.

URL: https://tracker.ceph.com/issues/48640
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

2 files changed, 30 insertions, 13 deletions

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index abbf48fc6230..570731c4d019 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -3047,6 +3047,7 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
 {
 	struct inode *inode = &ci->vfs_inode;
 	int last = 0, put = 0, flushsnaps = 0, wake = 0;
+	bool check_flushsnaps = false;
 
 	spin_lock(&ci->i_ceph_lock);
 	if (had & CEPH_CAP_PIN)
@@ -3063,26 +3064,17 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
 	if (had & CEPH_CAP_FILE_BUFFER) {
 		if (--ci->i_wb_ref == 0) {
 			last++;
+			/* put the ref held by ceph_take_cap_refs() */
 			put++;
+			check_flushsnaps = true;
 		}
 		dout("put_cap_refs %p wb %d -> %d (?)\n",
 		     inode, ci->i_wb_ref+1, ci->i_wb_ref);
 	}
-	if (had & CEPH_CAP_FILE_WR)
+	if (had & CEPH_CAP_FILE_WR) {
 		if (--ci->i_wr_ref == 0) {
 			last++;
-			if (__ceph_have_pending_cap_snap(ci)) {
-				struct ceph_cap_snap *capsnap =
-					list_last_entry(&ci->i_cap_snaps,
-							struct ceph_cap_snap,
-							ci_item);
-				capsnap->writing = 0;
-				if (ceph_try_drop_cap_snap(ci, capsnap))
-					put++;
-				else if (__ceph_finish_cap_snap(ci, capsnap))
-					flushsnaps = 1;
-				wake = 1;
-			}
+			check_flushsnaps = true;
 			if (ci->i_wrbuffer_ref_head == 0 &&
 			    ci->i_dirty_caps == 0 &&
 			    ci->i_flushing_caps == 0) {
@@ -3094,6 +3086,21 @@ static void __ceph_put_cap_refs(struct ceph_inode_info *ci, int had,
 			if (!__ceph_is_any_real_caps(ci) && ci->i_snap_realm)
 				drop_inode_snap_realm(ci);
 		}
+	}
+	if (check_flushsnaps && __ceph_have_pending_cap_snap(ci)) {
+		struct ceph_cap_snap *capsnap =
+			list_last_entry(&ci->i_cap_snaps,
+					struct ceph_cap_snap,
+					ci_item);
+
+		capsnap->writing = 0;
+		if (ceph_try_drop_cap_snap(ci, capsnap))
+			/* put the ref held by ceph_queue_cap_snap() */
+			put++;
+		else if (__ceph_finish_cap_snap(ci, capsnap))
+			flushsnaps = 1;
+		wake = 1;
+	}
 	spin_unlock(&ci->i_ceph_lock);
 
 	dout("put_cap_refs %p had %s%s%s\n", inode, ceph_cap_string(had),
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index b611f829cb61..0728b01d4d43 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -623,6 +623,16 @@ int __ceph_finish_cap_snap(struct ceph_inode_info *ci,
 		return 0;
 	}
 
+	/* Fb cap still in use, delay it */
+	if (ci->i_wb_ref) {
+		dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu "
+		     "used WRBUFFER, delaying\n", inode, capsnap,
+		     capsnap->context, capsnap->context->seq,
+		     ceph_cap_string(capsnap->dirty), capsnap->size);
+		capsnap->writing = 1;
+		return 0;
+	}
+
 	ci->i_ceph_flags |= CEPH_I_FLUSH_SNAPS;
 	dout("finish_cap_snap %p cap_snap %p snapc %p %llu %s s=%llu\n",
 	     inode, capsnap, capsnap->context,