From 4c021fa0343964268c03d1af627f6ece05b23fc9 Mon Sep 17 00:00:00 2001 From: Dilip Kumar Date: Sun, 15 Mar 2020 16:24:02 +0530 Subject: [PATCH v8 2/4] Add assert to ensure that page locks don't participate in deadlock cycle. Assert that we don't acquire any other heavyweight lock while holding the page lock except for relation extension. However, these locks are never taken in reverse order which implies that page locks will never participate in the deadlock cycle. Similar to relation extension, page locks are also held for a short duration, so imposing such a restriction won't hurt. Author: Dilip Kumar, with few changes by Amit Kapila Reviewed-by: Amit Kapila and Kuntal Ghosh Discussion: https://postgr.es/m/CAD21AoCmT3cFQUN4aVvzy5chw7DuzXrJCbrjTU05B+Ss=Gn1LA@mail.gmail.com --- src/backend/storage/lmgr/lock.c | 25 +++++++++++++++++++++++-- 1 file changed, 23 insertions(+), 2 deletions(-) diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index bad4e3a..7e65943 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -185,6 +185,18 @@ static int FastPathLocalUseCount = 0; */ static bool IsRelationExtensionLockHeld = false; +/* + * Flag to indicate if the page lock is held by this backend. We don't + * acquire any other heavyweight lock while holding the page lock except for + * relation extension. However, these locks are never taken in reverse order + * which implies that page locks will also never participate in the deadlock + * cycle. + * + * Similar to relation extension, page locks are also held for a short + * duration, so imposing such a restriction won't hurt. + */ +static bool IsPageLockHeld = false; + /* Macros for manipulating proc->fpLockBits */ #define FAST_PATH_BITS_PER_SLOT 3 #define FAST_PATH_LOCKNUMBER_OFFSET 1 @@ -863,6 +875,13 @@ LockAcquireExtended(const LOCKTAG *locktag, Assert(!IsRelationExtensionLockHeld); /* + * We don't acquire any other heavyweight lock while holding the page lock + * except for relation extension lock. + */ + Assert(!IsPageLockHeld || + (locktag->locktag_type == LOCKTAG_RELATION_EXTEND)); + + /* * Prepare to emit a WAL record if acquisition of this lock needs to be * replayed in a standby server. * @@ -1310,16 +1329,18 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc, } /* - * Check and set/reset the flag that we hold the relation extension lock. + * Check and set/reset the flag that we hold the relation extension/page lock. * * It is callers responsibility that this function is called after - * acquiring/releasing the relation extension lock. + * acquiring/releasing the relation extension/page lock. */ static inline void CheckAndSetLockHeld(LOCALLOCK *locallock, bool value) { if (LOCALLOCK_LOCKTAG(*locallock) == LOCKTAG_RELATION_EXTEND) IsRelationExtensionLockHeld = value; + else if (LOCALLOCK_LOCKTAG(*locallock) == LOCKTAG_PAGE) + IsPageLockHeld = value; } /* -- 1.8.3.1