This is a note to let you know that I've just added the patch titled ceph: do not update snapshot context when there is no new snapshot to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ceph-do-not-update-snapshot-context-when-there-is-no.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit e655095b18a368ff27abdd11a2bcdcad03e5599e Author: Xiubo Li <xiubli@xxxxxxxxxx> Date: Sat Feb 19 14:28:33 2022 +0800 ceph: do not update snapshot context when there is no new snapshot [ Upstream commit 2e586641c950e7f3e7e008404bd783a466b9b590 ] We will only track the uppest parent snapshot realm from which we need to rebuild the snapshot contexts _downward_ in hierarchy. For all the others having no new snapshot we will do nothing. This fix will avoid calling ceph_queue_cap_snap() on some inodes inappropriately. For example, with the code in mainline, suppose there are 2 directory hierarchies (with 6 directories total), like this: /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. Every time 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 the mds will send the kclient a snapshot backtrace in _downward_ order: seqs 4, 3. When ceph_update_snap_trace() is called, it will always rebuild the from the last realm, that's the root_snap. So later when rebuilding the snap context, the current logic will always cause it to rebuild the snap_X2 realm and then try to queue cap snaps for all the inodes related in that realm, even though it's not necessary. This is accompanied by a lot of these sorts of dout messages: "ceph: queue_cap_snap 00000000a42b796b nothing dirty|writing" Fix the logic to avoid this situation. Also, the 'invalidate' word is not precise here. In actuality, it will cause a rebuild of the existing snapshot contexts or just build non-existent ones. Rename it to 'rebuild_snapcs'. URL: https://tracker.ceph.com/issues/44100 Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx> Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx> Stable-dep-of: 51884d153f7e ("ceph: avoid putting the realm twice when decoding snaps fails") Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c index b41e6724c591..ae9cf37374e3 100644 --- a/fs/ceph/snap.c +++ b/fs/ceph/snap.c @@ -707,7 +707,8 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, __le64 *prior_parent_snaps; /* encoded */ struct ceph_snap_realm *realm = NULL; struct ceph_snap_realm *first_realm = NULL; - int invalidate = 0; + struct ceph_snap_realm *realm_to_rebuild = NULL; + int rebuild_snapcs; int err = -ENOMEM; LIST_HEAD(dirty_realms); @@ -715,6 +716,7 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, dout("update_snap_trace deletion=%d\n", deletion); more: + rebuild_snapcs = 0; ceph_decode_need(&p, e, sizeof(*ri), bad); ri = p; p += sizeof(*ri); @@ -738,7 +740,7 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, err = adjust_snap_realm_parent(mdsc, realm, le64_to_cpu(ri->parent)); if (err < 0) goto fail; - invalidate += err; + rebuild_snapcs += err; if (le64_to_cpu(ri->seq) > realm->seq) { dout("update_snap_trace updating %llx %p %lld -> %lld\n", @@ -763,22 +765,30 @@ int ceph_update_snap_trace(struct ceph_mds_client *mdsc, if (realm->seq > mdsc->last_snap_seq) mdsc->last_snap_seq = realm->seq; - invalidate = 1; + rebuild_snapcs = 1; } else if (!realm->cached_context) { dout("update_snap_trace %llx %p seq %lld new\n", realm->ino, realm, realm->seq); - invalidate = 1; + rebuild_snapcs = 1; } else { dout("update_snap_trace %llx %p seq %lld unchanged\n", realm->ino, realm, realm->seq); } - dout("done with %llx %p, invalidated=%d, %p %p\n", realm->ino, - realm, invalidate, p, e); + dout("done with %llx %p, rebuild_snapcs=%d, %p %p\n", realm->ino, + realm, rebuild_snapcs, p, e); - /* invalidate when we reach the _end_ (root) of the trace */ - if (invalidate && p >= e) - rebuild_snap_realms(realm, &dirty_realms); + /* + * this will always track the uppest parent realm from which + * we need to rebuild the snapshot contexts _downward_ in + * hierarchy. + */ + if (rebuild_snapcs) + realm_to_rebuild = realm; + + /* rebuild_snapcs when we reach the _end_ (root) of the trace */ + if (realm_to_rebuild && p >= e) + rebuild_snap_realms(realm_to_rebuild, &dirty_realms); if (!first_realm) first_realm = realm;