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Add wait-for-lsn process-exit cleanup callback

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WaitLSNCleanup() was called from ProcKill(), but not from
AuxiliaryProcKill(), even though xlogwait.c sizes its shared memory to
include NUM_AUXILIARY_PROCS and thus accepts calls from auxiliary
processes.  Such a process exiting while waiting would leave its entry in
the heap.

Register an on_shmem_exit callback lazily before a process enters a
wait-for-lsn heap instead, as suggested by Noah: that keeps the cleanup
local to xlogwait.c and makes it harder to miss a caller that needs it,
rather than having to remember every process-kill path.

Reported-by: Noah Misch <noah@leadboat.com>
Author: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Discussion: https://postgr.es/m/20260706012642.f9.noahmisch%40microsoft.com
Discussion: https://postgr.es/m/CABPTF7UtW_cAa%3DQh4RDfKiUqu3pJJE22ai9tbWJVERbeRyssLw%40mail.gmail.com
Backpatch-through: 19
This commit is contained in:
Alexander Korotkov
2026-08-18 14:24:21 +03:00
parent d02a9084d9
commit f994d2b71e
2 changed files with 38 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
src/backend/access/transam/xlogwait.c
View File

@@ -54,6 +54,7 @@
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/walreceiver.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/proc.h"
#include "storage/shmem.h"
@@ -69,8 +70,12 @@ static int waitlsn_cmp(const pairingheap_node *a, const pairingheap_node *b,
struct WaitLSNState *waitLSNState = NULL;
static bool waitLSNShmemExitRegistered = false;
static void WaitLSNShmemRequest(void *arg);
static void WaitLSNShmemInit(void *arg);
static void WaitLSNShmemExit(int code, Datum arg);
static void RegisterWaitLSNShmemExit(void);
const ShmemCallbacks WaitLSNShmemCallbacks = {
.request_fn = WaitLSNShmemRequest,
@@ -378,6 +383,31 @@ WaitLSNCleanup(void)
}
}
/*
* Exit callback to clean up any LSN wait state left behind if this process
* exits while waiting. Transaction abort paths call WaitLSNCleanup()
* directly.
*/
static void
WaitLSNShmemExit(int code, Datum arg)
{
WaitLSNCleanup();
}
/*
* Register shared-memory exit cleanup once per process. A backend may
* execute WAIT FOR LSN more than once.
*/
static void
RegisterWaitLSNShmemExit(void)
{
if (!waitLSNShmemExitRegistered)
{
on_shmem_exit(WaitLSNShmemExit, 0);
waitLSNShmemExitRegistered = true;
}
}
/*
* Check if the given LSN type requires recovery to be in progress.
* Standby wait types (replay, write, flush) require recovery;
@@ -412,6 +442,14 @@ WaitForLSN(WaitLSNType lsnType, XLogRecPtr targetLSN, int64 timeout)
/* Should have a valid proc number */
Assert(MyProcNumber >= 0 && MyProcNumber < MaxBackends + NUM_AUXILIARY_PROCS);
/*
* Ensure cleanup is registered before publishing our waiter entry.
* on_shmem_exit callbacks run in reverse registration order, so this
* callback runs before the earlier-registered ProcKill() and removes the
* entry before our PGPROC slot can be reused.
*/
RegisterWaitLSNShmemExit();
if (timeout > 0)
{
endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), timeout);

6
src/backend/storage/lmgr/proc.c
View File

@@ -37,7 +37,6 @@
#include "access/transam.h"
#include "access/twophase.h"
#include "access/xlogutils.h"
#include "access/xlogwait.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
@@ -965,11 +964,6 @@ ProcKill(int code, Datum arg)
*/
LWLockReleaseAll();
/*
* Cleanup waiting for LSN if any.
*/
WaitLSNCleanup();
/* Cancel any pending condition variable sleep, too */
ConditionVariableCancelSleep();