From: Xiubo Li <xiubli@xxxxxxxxxx> No need to update snapshot context when any of the following two cases happens: 1: if my context seq matches realm's seq and realm has no parent. 2: if my context seq equals or is larger than my parent's, this works because we rebuild_snap_realms() works _downward_ in hierarchy after each update. This fix will avoid those inodes which accidently calling ceph_queue_cap_snap() and make no sense, for exmaple: There have 6 directories like: /dir_X1/dir_X2/dir_X3/ /dir_Y1/dir_Y2/dir_Y3/ Firstly, make a snapshot under /dir_X1/dir_X2/.snap/snap_X2, then make a root snapshot under /.snap/root_snap. And every time when we make snapshots under /dir_Y1/..., the kclient will always try to rebuild the snap context for snap_X2 realm and finally will always try to queue cap snaps for dir_Y2 and dir_Y3, which makes no sense. That's because the snap_X2's seq is 2 and root_snap's seq is 3. So when creating a new snapshot under /dir_Y1/... the new seq will be 4, and then the mds will send kclient a snapshot backtrace in _downward_ in hierarchy: seqs 4, 3. Then in ceph_update_snap_trace() it will always rebuild the from the last realm, that's the root_snap. So later when rebuilding the snap context it will always rebuild the snap_X2 realm and then try to queue cap snaps for all the inodes related in snap_X2 realm, and we are seeing the logs like: "ceph: queue_cap_snap 00000000a42b796b nothing dirty|writing" URL: https://tracker.ceph.com/issues/44100 Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx> --- fs/ceph/snap.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c index d075d3ce5f6d..1f24a5de81e7 100644 --- a/fs/ceph/snap.c +++ b/fs/ceph/snap.c @@ -341,14 +341,16 @@ static int build_snap_context(struct ceph_snap_realm *realm, num += parent->cached_context->num_snaps; } - /* do i actually need to update? not if my context seq - matches realm seq, and my parents' does to. (this works - because we rebuild_snap_realms() works _downward_ in - hierarchy after each update.) */ + /* do i actually need to update? No need when any of the following + * two cases: + * #1: if my context seq matches realm's seq and realm has no parent. + * #2: if my context seq equals or is larger than my parent's, this + * works because we rebuild_snap_realms() works _downward_ in + * hierarchy after each update. + */ if (realm->cached_context && - realm->cached_context->seq == realm->seq && - (!parent || - realm->cached_context->seq >= parent->cached_context->seq)) { + ((realm->cached_context->seq == realm->seq && !parent) || + (parent && realm->cached_context->seq >= parent->cached_context->seq))) { dout("build_snap_context %llx %p: %p seq %lld (%u snaps)" " (unchanged)\n", realm->ino, realm, realm->cached_context, -- 2.27.0
