Re: Return pg_control from pg_backup_stop().

[Michael Paquier]

On Wed, Oct 28, 2026 at 09:00:44AM +0900, Michael Paquier wrote:
> Hearing nothing, I have added that into my own pipeline and applies
> the fix down to v15.  v14 has been left out, the branch going EOL soon
> with a problem that is extremely going to happen in practice does not
> give me a warm feeling.  For v15 and v16, I have backpatched
> d2c1e18de9d1 first.  The fix has been applied as of 4a92c8c29bd0.

Based on a sudden report from billbug, under Solaris 11, this gets
fun:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=billbug&dt=2026-10-28%2004%3A00%3A01

And we have a crash in a BASE_BACKUP command:
2026-10-28 05:23:30.548 CET [1429:4] LOG:  client backend (PID 1498)
was terminated by signal 11: Segmentation Fault
2026-10-28 05:23:30.548 CET [1429:5] DETAIL:  Failed process was
running: BASE_BACKUP ( LABEL 'pg_basebackup base backup',  PROGRESS,
CHECKPOINT 'fast',  WAIT 0,  TABLESPACE_MAP,  MANIFEST 'yes',  TARGET
'client')

This runs under valgrind with -DRELCACHE_FORCE_RELEASE, and of course
I am not able to reproduce it with combinations of these three.

The closest thing that I can see in recent history would be
040932c31146.  One possible explanation is PG_CONTROL_FILE_SIZE added
to the stack of perform_base_backup()?  I'm still puzzled without more
information from valgrind, but if that's right we could try a
palloc0() instead.

My blind suggestion of fix would be the attached, that I cannot really
test.  Thoughts or comments?
--
Michael

diff --git a/src/backend/backup/basebackup.c b/src/backend/backup/basebackup.c
index 0534ac217830..f8c3520e5b8e 100644
--- a/src/backend/backup/basebackup.c
+++ b/src/backend/backup/basebackup.c
@@ -347,7 +347,7 @@ perform_base_backup(basebackup_options *opt, bbsink *sink,
                                char       *backup_label;
                                ControlFileData *controlData;
                                bool            crc_ok;
-                               char            
controlFile[PG_CONTROL_FILE_SIZE];
+                               char       *controlFile;
 
                                bbsink_begin_archive(sink, "base.tar");
 
@@ -379,13 +379,14 @@ perform_base_backup(basebackup_options *opt, bbsink *sink,
                                                        (errmsg("calculated CRC 
checksum does not match value stored in file")));
 
                                /* Send the full file, zero-padded as it is on 
disk */
-                               memset(controlFile, 0, PG_CONTROL_FILE_SIZE);
+                               controlFile = palloc0(PG_CONTROL_FILE_SIZE);
                                memcpy(controlFile, controlData, 
sizeof(ControlFileData));
                                pfree(controlData);
 
                                sendFileWithContent(sink, XLOG_CONTROL_FILE,
                                                                        
controlFile, PG_CONTROL_FILE_SIZE,
                                                                        
&manifest);
+                               pfree(controlFile);
                        }
                        else
                        {

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