Merge 10.4 into 10.5

1 files changed, 13 insertions, 6 deletions

diff --git a/sql/log.cc b/sql/log.cc
index 98fb4a6d5a6..997434aa66b 100644
--- a/sql/log.cc
+++ b/sql/log.cc
@@ -7466,8 +7466,10 @@ MYSQL_BIN_LOG::queue_for_group_commit(group_commit_entry *orig_entry)
   */
   wfc= orig_entry->thd->wait_for_commit_ptr;
   orig_entry->queued_by_other= false;
-  if (wfc && wfc->waitee)
+  if (wfc && wfc->waitee.load(std::memory_order_acquire))
   {
+    wait_for_commit *loc_waitee;
+
     mysql_mutex_lock(&wfc->LOCK_wait_commit);
     /*
       Do an extra check here, this time safely under lock.
@@ -7479,10 +7481,10 @@ MYSQL_BIN_LOG::queue_for_group_commit(group_commit_entry *orig_entry)
       before setting the flag, so there is no risk that we can queue ahead of
       it.
     */
-    if (wfc->waitee && !wfc->waitee->commit_started)
+    if ((loc_waitee= wfc->waitee.load(std::memory_order_relaxed)) &&
+        !loc_waitee->commit_started)
     {
       PSI_stage_info old_stage;
-      wait_for_commit *loc_waitee;
 
       /*
         By setting wfc->opaque_pointer to our own entry, we mark that we are
@@ -7504,7 +7506,8 @@ MYSQL_BIN_LOG::queue_for_group_commit(group_commit_entry *orig_entry)
                                   &wfc->LOCK_wait_commit,
                                   &stage_waiting_for_prior_transaction_to_commit,
                                   &old_stage);
-      while ((loc_waitee= wfc->waitee) && !orig_entry->thd->check_killed(1))
+      while ((loc_waitee= wfc->waitee.load(std::memory_order_relaxed)) &&
+              !orig_entry->thd->check_killed(1))
         mysql_cond_wait(&wfc->COND_wait_commit, &wfc->LOCK_wait_commit);
       wfc->opaque_pointer= NULL;
       DBUG_PRINT("info", ("After waiting for prior commit, queued_by_other=%d",
@@ -7522,14 +7525,18 @@ MYSQL_BIN_LOG::queue_for_group_commit(group_commit_entry *orig_entry)
           do
           {
             mysql_cond_wait(&wfc->COND_wait_commit, &wfc->LOCK_wait_commit);
-          } while (wfc->waitee);
+          } while (wfc->waitee.load(std::memory_order_relaxed));
         }
         else
         {
           /* We were killed, so remove us from the list of waitee. */
           wfc->remove_from_list(&loc_waitee->subsequent_commits_list);
           mysql_mutex_unlock(&loc_waitee->LOCK_wait_commit);
-          wfc->waitee= NULL;
+          /*
+            This is the thread clearing its own status, it is no longer on
+            the list of waiters. So no memory barriers are needed here.
+          */
+          wfc->waitee.store(NULL, std::memory_order_relaxed);
 
           orig_entry->thd->EXIT_COND(&old_stage);
           /* Interrupted by kill. */