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MDEV-31448: Killing a replica thread awaiting its GCO can hang/crash a parallel replica

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The problem is that when a worker thread is (user) killed in
wait_for_prior_commit, the event group may complete out-of-order since the
wait for prior commit was aborted by the kill.

This fix ensures that event groups will always complete in-order, even
in the error case. This is done in finish_event_group() by doing an
extra wait_for_prior_commit(), if necessary, that ignores kills.

This fix supersedes the fix for MDEV-30780, so the earlier fix for
that is reverted in this patch.

Also fix that an error from wait_for_prior_commit() inside
finish_event_group() would not signal the error to
wakeup_subsequent_commits().

Based on earlier work by Brandon Nesterenko and Andrei Elkin, with
some changes to simplify the semantics of wait_for_prior_commit() and
make the code more robust to future changes.

Reviewed-by: Andrei Elkin <andrei.elkin@mariadb.com>
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>
This commit is contained in:
Kristian Nielsen
2023-06-15 21:35:53 +02:00
parent a8ea6627a4
commit 5d61442c85
3 changed files with 61 additions and 19 deletions
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10
sql/sql_class.h
View File

@@ -2144,14 +2144,14 @@ struct wait_for_commit
bool commit_started;
void register_wait_for_prior_commit(wait_for_commit *waitee);
int wait_for_prior_commit(THD *thd)
int wait_for_prior_commit(THD *thd, bool allow_kill=true)
{
/*
Quick inline check, to avoid function call and locking in the common case
where no wakeup is registered, or a registered wait was already signalled.
*/
if (waitee.load(std::memory_order_acquire))
return wait_for_prior_commit2(thd);
return wait_for_prior_commit2(thd, allow_kill);
else
{
if (wakeup_error)
@@ -2205,7 +2205,7 @@ struct wait_for_commit
void wakeup(int wakeup_error);
int wait_for_prior_commit2(THD *thd);
int wait_for_prior_commit2(THD *thd, bool allow_kill);
void wakeup_subsequent_commits2(int wakeup_error);
void unregister_wait_for_prior_commit2();
@@ -4726,10 +4726,10 @@ public:
}
wait_for_commit *wait_for_commit_ptr;
int wait_for_prior_commit()
int wait_for_prior_commit(bool allow_kill=true)
{
if (wait_for_commit_ptr)
return wait_for_commit_ptr->wait_for_prior_commit(this);
return wait_for_commit_ptr->wait_for_prior_commit(this, allow_kill);
return 0;
}
void wakeup_subsequent_commits(int wakeup_error)