diff options
| author | Andres Freund <andres@anarazel.de> | 2022-05-02 18:25:00 -0700 |
|---|---|---|
| committer | Andres Freund <andres@anarazel.de> | 2022-05-02 18:28:10 -0700 |
| commit | 57c5ad168be1ce9a5e91adb4c576996921cd8627 (patch) | |
| tree | b073616c253eaf447ff379e9493c42c84bea3a8b | |
| parent | 90abe1e17f9d3f725cf92a3ef43593ec56eaf671 (diff) | |
| download | postgresql-57c5ad168be1ce9a5e91adb4c576996921cd8627.tar.gz | |
Fix possibility of self-deadlock in ResolveRecoveryConflictWithBufferPin().
The tests added in 9f8a050f68d failed nearly reliably on FreeBSD in CI, and
occasionally on the buildfarm. That turns out to be caused not by a bug in the
test, but by a longstanding bug in recovery conflict handling.
The standby timeout handler, used by ResolveRecoveryConflictWithBufferPin(),
executed SendRecoveryConflictWithBufferPin() inside a signal handler. A bad
idea, because the deadlock timeout handler (or a spurious latch set) could
have interrupted ProcWaitForSignal(). If unlucky that could cause a
self-deadlock on ProcArrayLock, if the deadlock check is in
SendRecoveryConflictWithBufferPin()->CancelDBBackends().
To fix, set a flag in StandbyTimeoutHandler(), and check the flag in
ResolveRecoveryConflictWithBufferPin().
Subsequently the recovery conflict tests will be backpatched.
Discussion: https://postgr.es/m/20220413002626.udl7lll7f3o7nre7@alap3.anarazel.de
Backpatch: 10-
| -rw-r--r-- | src/backend/storage/ipc/standby.c | 22 |
1 files changed, 12 insertions, 10 deletions
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c index fdc4d4e61a..146b80db11 100644 --- a/src/backend/storage/ipc/standby.c +++ b/src/backend/storage/ipc/standby.c @@ -44,6 +44,7 @@ static HTAB *RecoveryLockLists; /* Flags set by timeout handlers */ static volatile sig_atomic_t got_standby_deadlock_timeout = false; +static volatile sig_atomic_t got_standby_delay_timeout = false; static volatile sig_atomic_t got_standby_lock_timeout = false; static void ResolveRecoveryConflictWithVirtualXIDs(VirtualTransactionId *waitlist, @@ -603,10 +604,15 @@ ResolveRecoveryConflictWithBufferPin(void) enable_timeouts(timeouts, cnt); } - /* Wait to be signaled by UnpinBuffer() */ + /* + * Wait to be signaled by UnpinBuffer() or for the wait to be interrupted + * by one of the timeouts established above. + */ ProcWaitForSignal(PG_WAIT_BUFFER_PIN); - if (got_standby_deadlock_timeout) + if (got_standby_delay_timeout) + SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN); + else if (got_standby_deadlock_timeout) { /* * Send out a request for hot-standby backends to check themselves for @@ -632,6 +638,7 @@ ResolveRecoveryConflictWithBufferPin(void) * individually, but that'd be slower. */ disable_all_timeouts(false); + got_standby_delay_timeout = false; got_standby_deadlock_timeout = false; } @@ -691,8 +698,8 @@ CheckRecoveryConflictDeadlock(void) */ /* - * StandbyDeadLockHandler() will be called if STANDBY_DEADLOCK_TIMEOUT - * occurs before STANDBY_TIMEOUT. + * StandbyDeadLockHandler() will be called if STANDBY_DEADLOCK_TIMEOUT is + * exceeded. */ void StandbyDeadLockHandler(void) @@ -702,16 +709,11 @@ StandbyDeadLockHandler(void) /* * StandbyTimeoutHandler() will be called if STANDBY_TIMEOUT is exceeded. - * Send out a request to release conflicting buffer pins unconditionally, - * so we can press ahead with applying changes in recovery. */ void StandbyTimeoutHandler(void) { - /* forget any pending STANDBY_DEADLOCK_TIMEOUT request */ - disable_timeout(STANDBY_DEADLOCK_TIMEOUT, false); - - SendRecoveryConflictWithBufferPin(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN); + got_standby_delay_timeout = true; } /* |