On Thu, 2021-08-12 at 12:10 +0800, xiubli@xxxxxxxxxx wrote:
> From: Xiubo Li <xiubli@xxxxxxxxxx>
>
> In case the export MDS is crashed just after the EImportStart journal
> is flushed, so when a standby MDS takes over it and when replaying
> the EImportStart journal the MDS will wait the client to reconnect,
> but the client may never register/open the sessions yet.
>
> We will try to reconnect that MDSes if they're in the export targets
> and in RECONNECT state.
>
> Signed-off-by: Xiubo Li <xiubli@xxxxxxxxxx>
> ---
> fs/ceph/mds_client.c | 58 +++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 57 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 14e44de05812..7dfe7a804320 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -4182,13 +4182,24 @@ static void check_new_map(struct ceph_mds_client *mdsc,
> struct ceph_mdsmap *newmap,
> struct ceph_mdsmap *oldmap)
> {
> - int i;
> + int i, err;
> + int *export_targets;
> int oldstate, newstate;
> struct ceph_mds_session *s;
> + struct ceph_mds_info *m_info;
>
> dout("check_new_map new %u old %u\n",
> newmap->m_epoch, oldmap->m_epoch);
>
> + m_info = newmap->m_info;
> + export_targets = kcalloc(newmap->possible_max_rank, sizeof(int), GFP_NOFS);
> + if (export_targets && m_info) {
> + for (i = 0; i < m_info->num_export_targets; i++) {
> + BUG_ON(m_info->export_targets[i] >= newmap->possible_max_rank);
In general, we shouldn't BUG() in response to bad info sent by the MDS.
It would probably be better to check these values in
ceph_mdsmap_decode() and return an error there if it doesn't look right.
That way we can just toss out the new map instead of crashing.
> + export_targets[m_info->export_targets[i]] = 1;
> + }
> + }
> +
> for (i = 0; i < oldmap->possible_max_rank && i < mdsc->max_sessions; i++) {
> if (!mdsc->sessions[i])
> continue;
> @@ -4242,6 +4253,8 @@ static void check_new_map(struct ceph_mds_client *mdsc,
> if (s->s_state == CEPH_MDS_SESSION_RESTARTING &&
> newstate >= CEPH_MDS_STATE_RECONNECT) {
> mutex_unlock(&mdsc->mutex);
> + if (export_targets)
> + export_targets[i] = 0;
> send_mds_reconnect(mdsc, s);
> mutex_lock(&mdsc->mutex);
> }
> @@ -4264,6 +4277,47 @@ static void check_new_map(struct ceph_mds_client *mdsc,
> }
> }
>
> + for (i = 0; i < newmap->possible_max_rank; i++) {
The condition on this loop is slightly different from the one below it,
and I'm not sure why. Should this also be checking this?
i < newmap->possible_max_rank && i < mdsc->max_sessions
...do we need to look at export targets where i >= mdsc->max_sessions ?
> + if (!export_targets)
> + break;
> +
> + /*
> + * Only open and reconnect sessions that don't
> + * exist yet.
> + */
> + if (!export_targets[i] || __have_session(mdsc, i))
> + continue;
> +
> + /*
> + * In case the export MDS is crashed just after
> + * the EImportStart journal is flushed, so when
> + * a standby MDS takes over it and is replaying
> + * the EImportStart journal the new MDS daemon
> + * will wait the client to reconnect it, but the
> + * client may never register/open the sessions
> + * yet.
> + *
> + * It will try to reconnect that MDS daemons if
> + * the MDSes are in the export targets and is the
> + * RECONNECT state.
> + */
> + newstate = ceph_mdsmap_get_state(newmap, i);
> + if (newstate != CEPH_MDS_STATE_RECONNECT)
> + continue;
> + s = __open_export_target_session(mdsc, i);
> + if (IS_ERR(s)) {
> + err = PTR_ERR(s);
> + pr_err("failed to open export target session, err %d\n",
> + err);
> + continue;
> + }
> + dout("send reconnect to target mds.%d\n", i);
> + mutex_unlock(&mdsc->mutex);
> + send_mds_reconnect(mdsc, s);
> + mutex_lock(&mdsc->mutex);
> + ceph_put_mds_session(s);
Suppose we end up in this part of the code, and we have to drop the
mdsc->mutex like this. What ensures that an earlier session in the array
won't end up going back into CEPH_MDS_STATE_RECONNECT before we can get
into the loop below? This looks racy.
> + }
> +
> for (i = 0; i < newmap->possible_max_rank && i < mdsc->max_sessions; i++) {
> s = mdsc->sessions[i];
> if (!s)
> @@ -4278,6 +4332,8 @@ static void check_new_map(struct ceph_mds_client *mdsc,
> __open_export_target_sessions(mdsc, s);
> }
> }
> +
> + kfree(export_targets);
> }
>
>
--
Jeff Layton <jlayton@xxxxxxxxxx>
