On 07/12/2022 22:20, Ilya Dryomov wrote:
On Wed, Dec 7, 2022 at 2:31 PM Xiubo Li <xiubli@xxxxxxxxxx> wrote:
On 07/12/2022 21:19, Xiubo Li wrote:
On 07/12/2022 18:59, Ilya Dryomov wrote:
On Tue, Dec 6, 2022 at 1:59 PM <xiubli@xxxxxxxxxx> wrote:
From: Xiubo Li <xiubli@xxxxxxxxxx>
When received corrupted snap trace we don't know what exactly has
happened in MDS side. And we shouldn't continue writing to OSD,
which may corrupt the snapshot contents.
Just try to blocklist this client and If fails we need to crash the
client instead of leaving it writeable to OSDs.
Cc: stable@xxxxxxxxxxxxxxx
URL: https://tracker.ceph.com/issues/57686
Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
---
Thanks Aaron's feedback.
V3:
- Fixed ERROR: spaces required around that ':' (ctx:VxW)
V2:
- Switched to WARN() to taint the Linux kernel.
fs/ceph/mds_client.c | 3 ++-
fs/ceph/mds_client.h | 1 +
fs/ceph/snap.c | 25 +++++++++++++++++++++++++
3 files changed, 28 insertions(+), 1 deletion(-)
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index cbbaf334b6b8..59094944af28 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -5648,7 +5648,8 @@ static void mds_peer_reset(struct
ceph_connection *con)
struct ceph_mds_client *mdsc = s->s_mdsc;
pr_warn("mds%d closed our session\n", s->s_mds);
- send_mds_reconnect(mdsc, s);
+ if (!mdsc->no_reconnect)
+ send_mds_reconnect(mdsc, s);
}
static void mds_dispatch(struct ceph_connection *con, struct
ceph_msg *msg)
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 728b7d72bf76..8e8f0447c0ad 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -413,6 +413,7 @@ struct ceph_mds_client {
atomic_t num_sessions;
int max_sessions; /* len of sessions
array */
int stopping; /* true if shutting
down */
+ int no_reconnect; /* true if snap trace
is corrupted */
atomic64_t quotarealms_count; /* # realms with
quota */
/*
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index c1c452afa84d..023852b7c527 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -767,8 +767,10 @@ int ceph_update_snap_trace(struct
ceph_mds_client *mdsc,
struct ceph_snap_realm *realm;
struct ceph_snap_realm *first_realm = NULL;
struct ceph_snap_realm *realm_to_rebuild = NULL;
+ struct ceph_client *client = mdsc->fsc->client;
int rebuild_snapcs;
int err = -ENOMEM;
+ int ret;
LIST_HEAD(dirty_realms);
lockdep_assert_held_write(&mdsc->snap_rwsem);
@@ -885,6 +887,29 @@ int ceph_update_snap_trace(struct
ceph_mds_client *mdsc,
if (first_realm)
ceph_put_snap_realm(mdsc, first_realm);
pr_err("%s error %d\n", __func__, err);
+
+ /*
+ * When receiving a corrupted snap trace we don't know what
+ * exactly has happened in MDS side. And we shouldn't continue
+ * writing to OSD, which may corrupt the snapshot contents.
+ *
+ * Just try to blocklist this kclient and if it fails we need
+ * to crash the kclient instead of leaving it writeable.
Hi Xiubo,
I'm not sure I understand this "let's blocklist ourselves" concept.
If the kernel client shouldn't continue writing to OSDs in this case,
why not just stop issuing writes -- perhaps initiating some equivalent
of a read-only remount like many local filesystems would do on I/O
errors (e.g. errors=remount-ro mode)?
The following patch seems working. Let me do more test to make sure
there is not further crash.
diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index c1c452afa84d..cd487f8a4cb5 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -767,6 +767,7 @@ int ceph_update_snap_trace(struct ceph_mds_client
*mdsc,
struct ceph_snap_realm *realm;
struct ceph_snap_realm *first_realm = NULL;
struct ceph_snap_realm *realm_to_rebuild = NULL;
+ struct super_block *sb = mdsc->fsc->sb;
int rebuild_snapcs;
int err = -ENOMEM;
LIST_HEAD(dirty_realms);
@@ -885,6 +886,9 @@ int ceph_update_snap_trace(struct ceph_mds_client
*mdsc,
if (first_realm)
ceph_put_snap_realm(mdsc, first_realm);
pr_err("%s error %d\n", __func__, err);
+ pr_err("Remounting filesystem read-only\n");
+ sb->s_flags |= SB_RDONLY;
+
return err;
}
For readonly approach is also my first thought it should be, but I was
just not very sure whether it would be the best approach.
Because by evicting the kclient we could prevent the buffer to be wrote
to OSDs. But the readonly one seems won't ?
The read-only setting is more for the VFS and the user. Technically,
the kernel client could just stop issuing writes (i.e. OSD requests
containing a write op) and not set SB_RDONLY. That should cover any
buffered data as well.
From reading the local exit4 and other fs, they all doing it this way
and the VFS will help stop further writing. Tested the above patch and
it worked as expected.
I think to stop the following OSD requests we can just check the
SB_RDONLY flag to prevent the buffer writeback.
By employing self-blocklisting, you are shifting the responsibility
of rejecting OSD requests to the OSDs. I'm saying that not issuing
OSD requests from a potentially busted client in the first place is
probably a better idea. At the very least you wouldn't need to BUG
on ceph_monc_blocklist_add() errors.
I found an issue for the read-only approach:
In read-only mode it still can access to the MDSs and OSDs, which will
continue trying to update the snap realms with the corrupted snap trace
as before when reading. What if users try to read or backup the
snapshots by using the corrupted snap realms ?
Isn't that a problem ?
Thanks
- Xiubo
Thanks,
Ilya
