[DaeMyung Kang <charsyam@gmail.com>]

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(-)

Attachments:

  [text/x-patch] 0001-Fix-EINTR-retry-condition-in-pg_flush_data-sync_file.patch (307B, ../20260429151811.1810874-1-charsyam@gmail.com/2-0001-Fix-EINTR-retry-condition-in-pg_flush_data-sync_file.patch)
  download | inline diff:
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;
 
 			/*