On Wed, Dec 28, 2016 at 10:01 AM, Andreas Seltenreich <seltenre...@gmx.de> wrote: > testing master as of fe591f8bf6 produced a crash reading > pg_stat_activity (backtrace below). Digging around with with gdb > revealed that pgstat_get_wait_event() returned an invalid pointer for a > classId PG_WAIT_LWLOCK. > > I think the culprit is dsa.c passing a pointer to memory that goes away > on dsa_free() as a name to LWLockRegisterTranche.
I see, nice detective work! dsa.c's create_internal and attach_internal call LWLockRegisterTranche with a pointer to a name in a DSM segment (copied from an argument to dsa_create), which doesn't have the right extent in this rare race case: the DSM segment goes away when the last backend detaches, but after you've detached you might still see others waiting for a lock that references that tranche ID in pg_stat_activity. This could be fixed by copying the tranche name to somewhere with backend lifetime extent in each backend, but then that would need cleanup. Maybe we should replace it with another value when the DSA area is detached, using a constant string. Something like LWLockRegisterTranche(tranche_id, "detached_dsa"). That would be a new use for the LWLockRegisterTranche function, for re-registering/renaming and existing tranche ID. Thoughts? -- Thomas Munro http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
