Hello Hackers,
I noticed a file descriptor leak when running PostgreSQL 18 with
io_method=io_uring. As far as I could tell, it only triggers when
the server restarts due to one of the backends being killed.
How to reproduce the issue:
- Setup a server configured with io_uring
- Check the number of open file descriptors:
ls -la "/proc/$(head -1 $PGDATA/postmaster.pid)/fd/" | grep "io_uring" | wc
-l
- SIGKILL a backend to trigger a server restart:
kill -9 $(psql -XtA -U postgres -c "SELECT pid FROM pg_stat_activity WHERE
backend_type = 'client backend' LIMIT 1")
- Check the number of open files descriptors again:
Expected: FD count remains the same.
Actual: FD count has doubled.
Tested on PostgreSQL 18.0, 18.1, 18.2, 18.3 and git master on the
following platforms:
- Ubuntu Server 24.04: Linux 6.8.0, liburing 2.5
- Exherbo Linux: Linux 6.16.12, liburing 2.12
- Fedora Linux: Linux 6.19.7, liburing 2.13-dev
>From what I could gather, this happens because
pgaio_uring_shmem_init() in
src/backend/storage/aio/method_io_uring.c doesn't cleanup
the allocated resources on exit.
I've attached a patch which registers an on_shmem_exit() callback
to close the file descriptors on server exit. I took inspiration
from how src/backend/storage/aio/method_worker.c handles cleanup.
Regards,
Lucas.
From 9728c2c28420677719e45139d9cbf16526cb1656 Mon Sep 17 00:00:00 2001
From: Lucas DRAESCHER <[email protected]>
Date: Tue, 17 Mar 2026 17:26:11 +0100
Subject: [PATCH v1] Release io_uring resources on shmem exit
io_uring_queue_init() allocates resources for each io_uring instance, but
pgaio_uring_shmem_init() never registered a cleanup callback to free them.
Add an on_shmem_exit() callback that calls io_uring_queue_exit().
The callback and its registration follow the same pattern as
pgaio_worker_die() in method_worker.c.
---
src/backend/storage/aio/method_io_uring.c | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)
diff --git a/src/backend/storage/aio/method_io_uring.c b/src/backend/storage/aio/method_io_uring.c
index 4867ded35ea..61984b798a9 100644
--- a/src/backend/storage/aio/method_io_uring.c
+++ b/src/backend/storage/aio/method_io_uring.c
@@ -37,6 +37,7 @@
#include "miscadmin.h"
#include "storage/aio_internal.h"
#include "storage/fd.h"
+#include "storage/ipc.h"
#include "storage/proc.h"
#include "storage/shmem.h"
#include "storage/lwlock.h"
@@ -277,6 +278,26 @@ pgaio_uring_shmem_size(void)
return sz;
}
+/*
+ * on_shmem_exit() callback that releases the io_uring queues in
+ * pgaio_uring_shmem_init.
+ */
+static void
+pgaio_uring_die(int code, Datum arg)
+{
+ if (pgaio_uring_contexts != NULL)
+ {
+ int TotalProcs = pgaio_uring_procs();
+
+ elog(DEBUG1, "cleaning up %d io_uring processes", TotalProcs);
+
+ for (int i = 0; i < TotalProcs; i++)
+ io_uring_queue_exit(&pgaio_uring_contexts[i].io_uring_ring);
+
+ pgaio_uring_contexts = NULL;
+ }
+}
+
static void
pgaio_uring_shmem_init(bool first_time)
{
@@ -393,6 +414,8 @@ pgaio_uring_shmem_init(bool first_time)
LWLockInitialize(&context->completion_lock, LWTRANCHE_AIO_URING_COMPLETION);
}
+
+ on_shmem_exit(pgaio_uring_die, 0);
}
static void
--
2.53.0
