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[email protected]
Discussion: https://postgr.es/m/CA%2BhUKGJ31Wce6HJ7xnVTKWjFUWQZPBngxfJVx4q0E98pDr3kAw%40mail.gmail.com

diff --git a/src/backend/lib/dshash.c b/src/backend/lib/dshash.c
index 782b509fd9f342ec4d793edb7447bcc006e62b4e..ab56a45d20c881e8b9783f10fc7d3f6da84f8a19 100644 (file)
--- 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);
@@ -410,8 +407,6 @@ dshash_find(dshash_table *hash_table, const void *key, bool exclusive)
    else
    {
        /* The caller will free the lock by calling dshash_release_lock. */
-       hash_table->find_locked = true;
-       hash_table->find_exclusively_locked = exclusive;
        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 cf255abbb768cbdc65c4a22902970e3f52bc0c77..365d215f2bc989df37a3a347a2e5c68f7d05a909 100644 (file)
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -1941,6 +1941,32 @@ 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 c04ae971485e311c741c6332232382e39573422f..cdbfbed118375e0ac4ad23553e6019fadfc29fb0 100644 (file)
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -149,6 +149,7 @@ 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);