injection_points: Add proper locking when reporting fixed-variable stats

Contrary to its siblings for the archiver, the bgwriter and the
checkpointer stats, pgstat_report_inj_fixed() can be called
concurrently.  This was causing an assertion failure, while messing up
with the stats.

This code is aimed at being a template for extension developers, so it
is not a critical issue, but let's be correct.  This module has also
been useful for some benchmarking, at least for me, and that was how I
have discovered this issue.

Oversight in f68cd847fa40.

Author: Michael Paquier <[email protected]>
Reviewed-by: Bertrand Drouvot <[email protected]>
Reviewed-by: Chao Li <[email protected]>
Reviewed-by: wenhui qiu <[email protected]>
Discussion: https://postgr.es/m/[email protected]
Backpatch-through: 18

diff --git a/src/test/modules/injection_points/injection_stats_fixed.c b/src/test/modules/injection_points/injection_stats_fixed.c
index bc54c79d190b9b63f07842a75f6956686ef932ad..74c35fcbfa711b546341102049fbbec1937957a8 100644 (file)
--- a/src/test/modules/injection_points/injection_stats_fixed.c
+++ b/src/test/modules/injection_points/injection_stats_fixed.c
@@ -152,6 +152,8 @@ pgstat_report_inj_fixed(uint32 numattach,
 
    stats_shmem = pgstat_get_custom_shmem_data(PGSTAT_KIND_INJECTION_FIXED);
 
+   LWLockAcquire(&stats_shmem->lock, LW_EXCLUSIVE);
+
    pgstat_begin_changecount_write(&stats_shmem->changecount);
    stats_shmem->stats.numattach += numattach;
    stats_shmem->stats.numdetach += numdetach;
@@ -159,6 +161,8 @@ pgstat_report_inj_fixed(uint32 numattach,
    stats_shmem->stats.numcached += numcached;
    stats_shmem->stats.numloaded += numloaded;
    pgstat_end_changecount_write(&stats_shmem->changecount);
+
+   LWLockRelease(&stats_shmem->lock);
 }
 
 /*