On 8/18/21 12:18 AM, Jeff Layton wrote:
On Tue, 2021-08-17 at 11:44 +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>
---
- check the export target rank when decoding the mdsmap instead of
BUG_ON
- fix issue that the sessions have been opened during the mutex's
unlock/lock gap
fs/ceph/mds_client.c | 63 +++++++++++++++++++++++++++++++++++++++++++-
fs/ceph/mdsmap.c | 10 ++++---
2 files changed, 69 insertions(+), 4 deletions(-)
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index e49dbeb6c06f..1e013fb09d73 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -4197,13 +4197,22 @@ 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);
This allocation could fail under low-memory conditions, particularly
since it's GFP_NOFS. One idea would be to make this function return int
so you can just return -ENOMEM if the allocation fails.
Is there a hard max to possible_max_rank? If so and it's not that big,
then another possibility would be to just declare this array on the
stack.
Also, since this is just used as a flag, making an array of bools would
reduce the size of the allocation by a factor of 4.
I think the CEPH_MAX_MDS is, it's 0x100. I will try the bitmap on the stack.
+ if (export_targets && m_info) {
+ for (i = 0; i < m_info->num_export_targets; i++)
+ export_targets[m_info->export_targets[i]] = 1;
+ }
+
If you reverse the sense of the flags then you wouldn't need to
initialize the array at all (assuming you still use kcalloc).
For example the size of the export_targets array is 100, and the
num_export_target is 1 and the m_info->export_targets[0] is 7, then we
must clear all the other 99 flags one by one ?
for (i = 0; i < oldmap->possible_max_rank && i < mdsc->max_sessions; i++) {
if (!mdsc->sessions[i])
continue;
@@ -4257,6 +4266,8 @@ 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);
}
@@ -4279,6 +4290,54 @@ static void check_new_map(struct ceph_mds_client *mdsc,
}
}
+ /*
+ * Only open and reconnect sessions that don't exist yet.
+ */
+ for (i = 0; i < newmap->possible_max_rank; i++) {
+ if (unlikely(!export_targets))
+ break;
+
+ /*
+ * In case the import 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 session yet.
+ *
+ * Will try to reconnect that MDS daemon if the
+ * rank number is in the export_targets array and
+ * is the up:reconnect state.
+ */
+ newstate = ceph_mdsmap_get_state(newmap, i);
+ if (!export_targets[i] || newstate != CEPH_MDS_STATE_RECONNECT)
+ continue;
+
+ /*
+ * The session maybe registered and opened by some
+ * requests which were choosing random MDSes during
+ * the mdsc->mutex's unlock/lock gap below in rare
+ * case. But the related MDS daemon will just queue
+ * that requests and be still waiting for the client's
+ * reconnection request in up:reconnect state.
+ */
+ s = __ceph_lookup_mds_session(mdsc, i);
+ if (likely(!s)) {
+ 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 export target mds.%d\n", i);
+ mutex_unlock(&mdsc->mutex);
+ send_mds_reconnect(mdsc, s);
+ mutex_lock(&mdsc->mutex);
+ ceph_put_mds_session(s);
You can put the mds session before you re-take the mutex.
Will fix it.
Thanks
