From e5986a551ec0a8a8289ca1273c383a8ec4834e23 Mon Sep 17 00:00:00 2001 From: Dilip Kumar Date: Mon, 16 Mar 2020 09:22:58 +0530 Subject: [PATCH v10 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 | 27 +++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index 34a7ed9..6a4bda57 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -187,6 +187,20 @@ static int FastPathLocalUseCount = 0; static bool IsRelationExtensionLockHeld = false; #endif +/* + * 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. + */ +#ifdef USE_ASSERT_CHECKING +static bool IsPageLockHeld = false; +#endif + /* Macros for manipulating proc->fpLockBits */ #define FAST_PATH_BITS_PER_SLOT 3 #define FAST_PATH_LOCKNUMBER_OFFSET 1 @@ -865,6 +879,13 @@ 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. * @@ -1312,10 +1333,10 @@ 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. * * Pass acquired = true if lock is acquired, false otherwise. */ @@ -1325,6 +1346,8 @@ CheckAndSetLockHeld(LOCALLOCK *locallock, bool acquired) { if (LOCALLOCK_LOCKTAG(*locallock) == LOCKTAG_RELATION_EXTEND) IsRelationExtensionLockHeld = acquired; + else if (LOCALLOCK_LOCKTAG(*locallock) == LOCKTAG_PAGE) + IsPageLockHeld = acquired; } #endif -- 1.8.3.1