mds: fix issuing redundant reintegrate/migrate_stray requests

Just in case a CInode's nlink is 1, and then a unlink request comes
and then early replies and submits to the MDLogs, but just before
the MDlogs are flushed a link request comes, and the link request
also succeeds and early replies to client.

Later when the unlink/link requests' MDLog events are flushed and
the callbacks are called, which will fire a stray denty reintegration.
But it will pick the new dentry, which is from the link's request
and is a remote dentry, to do the reintegration. While in the
'rename' code when traversing the path it will trigger to call the
'dn->link_remote()', which later will fire a new stray dentry
reintegration.

The problem is if the first 'rename' request is retried several
times, and in each time it will fire a new reintegration, which
makes no sense and maybe blocked for a very long time dues to some
reasons and then will be reported as slow request warning.

Fixes: https://tracker.ceph.com/issues/62702
Signed-off-by: Xiubo Li <xiubli@redhat.com>

src/mds/CDentry.h

@@ -376,6 +376,8 @@ class CDentry : public MDSCacheObject, public LRUObject, public Counter<CDentry>
   mempool::mds_co::map<client_t,ClientLease*> client_lease_map;
   std::map<int, std::unique_ptr<BatchOp>> batch_ops;
 
+  ceph_tid_t reintegration_reqid = 0;
+
 
 protected:
   friend class Migrator;

src/mds/MDSRank.h

@@ -160,8 +160,10 @@ struct MDSMetaRequest {
   explicit MDSMetaRequest(int o, CDentry *d, ceph_tid_t t) :
     op(o), dentry(d), tid(t) {
     dentry->get(CDentry::PIN_PURGING);
+    dentry->reintegration_reqid = tid;
   }
   ~MDSMetaRequest() {
+    dentry->reintegration_reqid = 0;
     dentry->put(CDentry::PIN_PURGING);
   }
 

src/mds/StrayManager.cc

@@ -673,6 +673,12 @@ void StrayManager::reintegrate_stray(CDentry *straydn, CDentry *rdn)
 {
   dout(10) << __func__ << " " << *straydn << " to " << *rdn << dendl;
 
+  if (straydn->reintegration_reqid) {
+    dout(20) << __func__ << ": stray dentry " << *straydn
+             << " is already under reintegrating" << dendl;
+    return;
+  }
+
   logger->inc(l_mdc_strays_reintegrated);
 
   // rename it to remote linkage .
@@ -698,6 +704,12 @@ void StrayManager::migrate_stray(CDentry *dn, mds_rank_t to)
 {
   dout(10) << __func__ << " " << *dn << " to mds." << to << dendl;
 
+  if (dn->reintegration_reqid) {
+    dout(20) << __func__ << ": stray dentry " << *dn
+             << " is already under migrating" << dendl;
+    return;
+  }
+
   logger->inc(l_mdc_strays_migrated);
 
   // rename it to another mds.