Hi,
I noticed sporadic segfaults when selecting from pg_stat_activity on
current HEAD.
The culprit is the 53be0b1add7064ca5db3cd884302dfc3268d884e commit which
added more wait info into the pg_stat_get_activity(). More specifically,
the following code is broken:
+ proc = BackendPidGetProc(beentry->st_procpid);
+ wait_event_type =
pgstat_get_wait_event_type(proc->wait_event_info);
This needs to check if proc is NULL. When reading the code I noticed
that the new functions pg_stat_get_backend_wait_event_type() and
pg_stat_get_backend_wait_event() suffer from the same problem.
Here is PoC patch which fixes the problem. I am wondering if we should
raise warning in the pg_stat_get_backend_wait_event_type() and
pg_stat_get_backend_wait_event() like the pg_signal_backend() does when
proc is NULL instead of just returning NULL which is what this patch
does though.
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 64c4cc4..355e58c 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -783,13 +783,23 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
values[5] = CStringGetTextDatum(beentry->st_activity);
proc = BackendPidGetProc(beentry->st_procpid);
- wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info);
+ if (proc != NULL)
+ {
+ wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info);
+ wait_event = pgstat_get_wait_event(proc->wait_event_info);
+
+ }
+ else
+ {
+ wait_event_type = NULL;
+ wait_event = NULL;
+ }
+
if (wait_event_type)
values[6] = CStringGetTextDatum(wait_event_type);
else
nulls[6] = true;
- wait_event = pgstat_get_wait_event(proc->wait_event_info);
if (wait_event)
values[7] = CStringGetTextDatum(wait_event);
else
@@ -990,11 +1000,8 @@ pg_stat_get_backend_wait_event_type(PG_FUNCTION_ARGS)
wait_event_type = "<backend information not available>";
else if (!has_privs_of_role(GetUserId(), beentry->st_userid))
wait_event_type = "<insufficient privilege>";
- else
- {
- proc = BackendPidGetProc(beentry->st_procpid);
+ else if ((proc = BackendPidGetProc(beentry->st_procpid)) != NULL)
wait_event_type = pgstat_get_wait_event_type(proc->wait_event_info);
- }
if (!wait_event_type)
PG_RETURN_NULL();
@@ -1014,11 +1021,8 @@ pg_stat_get_backend_wait_event(PG_FUNCTION_ARGS)
wait_event = "<backend information not available>";
else if (!has_privs_of_role(GetUserId(), beentry->st_userid))
wait_event = "<insufficient privilege>";
- else
- {
- proc = BackendPidGetProc(beentry->st_procpid);
+ else if ((proc = BackendPidGetProc(beentry->st_procpid)) != NULL)
wait_event = pgstat_get_wait_event(proc->wait_event_info);
- }
if (!wait_event)
PG_RETURN_NULL();
--
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