From: DaeMyung Kang <charsyam@gmail.com>
To: pgsql-hackers@lists.postgresql.org
Cc: DaeMyung Kang <charsyam@gmail.com>
Subject: [PATCH] Fix EINTR retry condition in pg_flush_data sync_file_range
 path.
Date: Thu, 30 Apr 2026 00:18:11 +0900
Message-ID: <20260429151811.1810874-1-charsyam@gmail.com>
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Hi, Hackers,

While auditing src/backend/storage/file, I spotted a small but
unambiguous bug in pg_flush_data()'s sync_file_range() retry path.
Details below in the commit message; the fix is a one-token change.

Thanks,
DaeMyung

---

The retry branch compared the syscall return value (rc) against EINTR,
but sync_file_range() returns -1 on error and reports the actual errno
out-of-band, so rc == EINTR was always false and the retry was dead
code.  When sync_file_range() was actually interrupted by a signal,
control fell through to the warning/error path instead of retrying.

Compare errno instead, matching the convention already used elsewhere
in this file (e.g. the pg_pread/pg_pwrite EINTR retries) and a few
lines down for ENOSYS in this same block.
---
 src/backend/storage/file/fd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


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diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index a8be066afe0..817855e2720 100644
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -563,7 +563,7 @@ retry:
 		{
 			int			elevel;
 
-			if (rc == EINTR)
+			if (errno == EINTR)
 				goto retry;
 
 			/*

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