From 4f88dbac22a845a33c758554e25ca0ee7e9dedac Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Mon, 11 Jul 2022 14:47:16 +1200 Subject: [PATCH] Fix lock assertions in dshash.c. dshash.c previously maintained flags to be able to assert that you didn't hold any partition lock. These flags could get out of sync with reality in error scenarios. Get rid of all that, and make assertions about the locks themselves instead. Since LWLockHeldByMe() loops internally, we don't want to put that inside another loop over all partition locks. Introduce a new debugging-only interface LWLockAnyHeldByMe() to avoid that. This problem was noted by Tom and Andres while reviewing changes to support the new shared memory stats system, and later showed up in reality while working on commit 389869af. Back-patch to 11, where dshash.c arrived. Reported-by: Tom Lane Reported-by: Andres Freund Reviewed-by: Kyotaro HORIGUCHI Reviewed-by: Zhihong Yu Reviewed-by: Andres Freund Discussion: https://postgr.es/m/20220311012712.botrpsikaufzteyt@alap3.anarazel.de Discussion: https://postgr.es/m/CA%2BhUKGJ31Wce6HJ7xnVTKWjFUWQZPBngxfJVx4q0E98pDr3kAw%40mail.gmail.com --- src/backend/lib/dshash.c | 37 +++++++++---------------------- src/backend/storage/lmgr/lwlock.c | 26 ++++++++++++++++++++++ src/include/storage/lwlock.h | 1 + 3 files changed, 37 insertions(+), 27 deletions(-) diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c index 557676ad38..c0ab709c03 100644 --- a/src/backend/lib/dshash.c +++ b/src/backend/lib/dshash.c @@ -110,8 +110,6 @@ struct dshash_table dshash_table_control *control; /* Control object in DSM. */ dsa_pointer *buckets; /* Current bucket pointers in DSM. */ size_t size_log2; /* log2(number of buckets) */ - bool find_locked; /* Is any partition lock held by 'find'? */ - bool find_exclusively_locked; /* ... exclusively? */ }; /* Given a pointer to an item, find the entry (user data) it holds. */ @@ -186,6 +184,10 @@ static inline bool equal_keys(dshash_table *hash_table, #define PARTITION_LOCK(hash_table, i) \ (&(hash_table)->control->partitions[(i)].lock) +#define ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table) \ + Assert(!LWLockAnyHeldByMe(&(hash_table)->control->partitions[0].lock, \ + DSHASH_NUM_PARTITIONS, sizeof(dshash_partition))) + /* * Create a new hash table backed by the given dynamic shared area, with the * given parameters. The returned object is allocated in backend-local memory @@ -226,9 +228,6 @@ dshash_create(dsa_area *area, const dshash_parameters *params, void *arg) } } - hash_table->find_locked = false; - hash_table->find_exclusively_locked = false; - /* * Set up the initial array of buckets. Our initial size is the same as * the number of partitions. @@ -277,8 +276,6 @@ dshash_attach(dsa_area *area, const dshash_parameters *params, hash_table->params = *params; hash_table->arg = arg; hash_table->control = dsa_get_address(area, control); - hash_table->find_locked = false; - hash_table->find_exclusively_locked = false; Assert(hash_table->control->magic == DSHASH_MAGIC); /* @@ -301,7 +298,7 @@ dshash_attach(dsa_area *area, const dshash_parameters *params, void dshash_detach(dshash_table *hash_table) { - Assert(!hash_table->find_locked); + ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table); /* The hash table may have been destroyed. Just free local memory. */ pfree(hash_table); @@ -392,7 +389,7 @@ dshash_find(dshash_table *hash_table, const void *key, bool exclusive) partition = PARTITION_FOR_HASH(hash); Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(!hash_table->find_locked); + ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table); LWLockAcquire(PARTITION_LOCK(hash_table, partition), exclusive ? LW_EXCLUSIVE : LW_SHARED); @@ -409,9 +406,7 @@ dshash_find(dshash_table *hash_table, const void *key, bool exclusive) } else { - /* The caller will free the lock by calling dshash_release. */ - hash_table->find_locked = true; - hash_table->find_exclusively_locked = exclusive; + /* The caller will free the lock by calling dshash_release_lock. */ return ENTRY_FROM_ITEM(item); } } @@ -441,7 +436,7 @@ dshash_find_or_insert(dshash_table *hash_table, partition = &hash_table->control->partitions[partition_index]; Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(!hash_table->find_locked); + ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table); restart: LWLockAcquire(PARTITION_LOCK(hash_table, partition_index), @@ -486,8 +481,6 @@ restart: } /* The caller must release the lock with dshash_release_lock. */ - hash_table->find_locked = true; - hash_table->find_exclusively_locked = true; return ENTRY_FROM_ITEM(item); } @@ -506,7 +499,7 @@ dshash_delete_key(dshash_table *hash_table, const void *key) bool found; Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(!hash_table->find_locked); + ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table); hash = hash_key(hash_table, key); partition = PARTITION_FOR_HASH(hash); @@ -543,14 +536,10 @@ dshash_delete_entry(dshash_table *hash_table, void *entry) size_t partition = PARTITION_FOR_HASH(item->hash); Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(hash_table->find_locked); - Assert(hash_table->find_exclusively_locked); Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition), LW_EXCLUSIVE)); delete_item(hash_table, item); - hash_table->find_locked = false; - hash_table->find_exclusively_locked = false; LWLockRelease(PARTITION_LOCK(hash_table, partition)); } @@ -564,13 +553,7 @@ dshash_release_lock(dshash_table *hash_table, void *entry) size_t partition_index = PARTITION_FOR_HASH(item->hash); Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(hash_table->find_locked); - Assert(LWLockHeldByMeInMode(PARTITION_LOCK(hash_table, partition_index), - hash_table->find_exclusively_locked - ? LW_EXCLUSIVE : LW_SHARED)); - hash_table->find_locked = false; - hash_table->find_exclusively_locked = false; LWLockRelease(PARTITION_LOCK(hash_table, partition_index)); } @@ -603,7 +586,7 @@ dshash_dump(dshash_table *hash_table) size_t j; Assert(hash_table->control->magic == DSHASH_MAGIC); - Assert(!hash_table->find_locked); + ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(hash_table); for (i = 0; i < DSHASH_NUM_PARTITIONS; ++i) { diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index 92e4fc7b0b..6b6e920704 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -1843,6 +1843,32 @@ LWLockHeldByMe(LWLock *l) return false; } +/* + * LWLockHeldByMe - test whether my process holds any of an array of locks + * + * This is meant as debug support only. + */ +bool +LWLockAnyHeldByMe(LWLock *l, int nlocks, size_t stride) +{ + char *held_lock_addr; + char *begin; + char *end; + int i; + + begin = (char *) l; + end = begin + nlocks * stride; + for (i = 0; i < num_held_lwlocks; i++) + { + held_lock_addr = (char *) held_lwlocks[i].lock; + if (held_lock_addr >= begin && + held_lock_addr < end && + (held_lock_addr - begin) % stride == 0) + return true; + } + return false; +} + /* * LWLockHeldByMeInMode - test whether my process holds a lock in given mode * diff --git a/src/include/storage/lwlock.h b/src/include/storage/lwlock.h index 08e0dc8144..87b1ce083d 100644 --- a/src/include/storage/lwlock.h +++ b/src/include/storage/lwlock.h @@ -150,6 +150,7 @@ extern void LWLockRelease(LWLock *lock); extern void LWLockReleaseClearVar(LWLock *lock, uint64 *valptr, uint64 val); extern void LWLockReleaseAll(void); extern bool LWLockHeldByMe(LWLock *lock); +extern bool LWLockAnyHeldByMe(LWLock *lock, int nlocks, size_t stride); extern bool LWLockHeldByMeInMode(LWLock *lock, LWLockMode mode); extern bool LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval);