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 <[email protected]>
Reported-by: Andres Freund <[email protected]>
Reviewed-by: Kyotaro HORIGUCHI <[email protected]>
Reviewed-by: Zhihong Yu <[email protected]>
Reviewed-by: Andres Freund <[email protected]>
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 ec454b4d65589aed2ae518bc79302a5d852a2c05..c5c032a593b1c9489faba0d0af2b669ac8e9256c 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. */
@@ -194,6 +192,10 @@ 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
@@ -234,9 +236,6 @@ 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.
@@ -285,8 +284,6 @@ 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);
 
    /*
@@ -309,7 +306,7 @@ 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);
@@ -400,7 +397,7 @@ 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);
@@ -418,8 +415,6 @@ 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);
    }
 }
@@ -449,7 +444,7 @@ 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),
@@ -494,8 +489,6 @@ 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);
 }
 
@@ -514,7 +507,7 @@ 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);
@@ -551,14 +544,10 @@ 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));
 }
 
@@ -572,13 +561,7 @@ 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));
 }
 
@@ -644,7 +627,7 @@ dshash_seq_next(dshash_seq_status *status)
    if (status->curpartition == -1)
    {
        Assert(status->curbucket == 0);
-       Assert(!status->hash_table->find_locked);
+       ASSERT_NO_PARTITION_LOCKS_HELD_BY_ME(status->hash_table);
 
        status->curpartition = 0;
 
@@ -702,8 +685,6 @@ dshash_seq_next(dshash_seq_status *status)
 
    status->curitem =
        dsa_get_address(status->hash_table->area, next_item_pointer);
-   status->hash_table->find_locked = true;
-   status->hash_table->find_exclusively_locked = status->exclusive;
 
    /*
     * The caller may delete the item. Store the next item in case of
@@ -722,9 +703,6 @@ dshash_seq_next(dshash_seq_status *status)
 void
 dshash_seq_term(dshash_seq_status *status)
 {
-   status->hash_table->find_locked = false;
-   status->hash_table->find_exclusively_locked = false;
-
    if (status->curpartition >= 0)
        LWLockRelease(PARTITION_LOCK(status->hash_table, status->curpartition));
 }
@@ -743,8 +721,6 @@ dshash_delete_current(dshash_seq_status *status)
 
    Assert(status->exclusive);
    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));
 
@@ -762,7 +738,7 @@ 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 fc5c76a48f8762e7e034461f63c3c9ec7be913c2..38317edaf96f0c3a292561ecbfcd01f4fbea3b2f 100644 (file)
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -1925,6 +1925,32 @@ 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 52b32bda9919c083ea5087cd90129ebc82f1de29..e03d317eeac744a5ca2fe18992b3572619e59bad 100644 (file)
--- a/src/include/storage/lwlock.h
+++ b/src/include/storage/lwlock.h
@@ -120,6 +120,7 @@ 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);