@@ -151,6 +151,22 @@ struct qht_bucket {
QEMU_BUILD_BUG_ON(sizeof(struct qht_bucket) > QHT_BUCKET_ALIGN);
+/*
+ * Under TSAN, we use striped locks instead of one lock per bucket chain.
+ * This avoids crashing under TSAN, since TSAN aborts the program if more than
+ * 64 locks are held (this is a hardcoded limit in TSAN).
+ * When resizing a QHT we grab all the buckets' locks, which can easily
+ * go over TSAN's limit. By using striped locks, we avoid this problem.
+ *
+ * Note: this number must be a power of two for easy index computation.
+ */
+#define QHT_TSAN_BUCKET_LOCKS_BITS 4
+#define QHT_TSAN_BUCKET_LOCKS (1 << QHT_TSAN_BUCKET_LOCKS_BITS)
+
+struct qht_tsan_lock {
+ QemuSpin lock;
+} QEMU_ALIGNED(QHT_BUCKET_ALIGN);
+
/**
* struct qht_map - structure to track an array of buckets
* @rcu: used by RCU. Keep it as the top field in the struct to help valgrind
@@ -160,6 +176,7 @@ QEMU_BUILD_BUG_ON(sizeof(struct qht_bucket) > QHT_BUCKET_ALIGN);
* @n_added_buckets: number of added (i.e. "non-head") buckets
* @n_added_buckets_threshold: threshold to trigger an upward resize once the
* number of added buckets surpasses it.
+ * @tsan_bucket_locks: Array of striped locks to be used only under TSAN.
*
* Buckets are tracked in what we call a "map", i.e. this structure.
*/
@@ -169,6 +186,9 @@ struct qht_map {
size_t n_buckets;
size_t n_added_buckets;
size_t n_added_buckets_threshold;
+#ifdef CONFIG_TSAN
+ struct qht_tsan_lock tsan_bucket_locks[QHT_TSAN_BUCKET_LOCKS];
+#endif
};
/* trigger a resize when n_added_buckets > n_buckets / div */
@@ -229,10 +249,68 @@ static inline size_t qht_elems_to_buckets(size_t n_elems)
return pow2ceil(n_elems / QHT_BUCKET_ENTRIES);
}
-static inline void qht_head_init(struct qht_bucket *b)
+/*
+ * When using striped locks (i.e. under TSAN), we have to be careful not
+ * to operate on the same lock twice (e.g. when iterating through all buckets).
+ * We achieve this by operating only on each stripe's first matching lock.
+ */
+static inline void qht_do_if_first_in_stripe(const struct qht_map *map,
+ struct qht_bucket *b,
+ void (*func)(QemuSpin *spin))
+{
+#ifdef CONFIG_TSAN
+ unsigned long bucket_idx = b - map->buckets;
+ bool is_first_in_stripe = (bucket_idx >> QHT_TSAN_BUCKET_LOCKS_BITS) == 0;
+ if (is_first_in_stripe) {
+ unsigned long lock_idx = bucket_idx & (QHT_TSAN_BUCKET_LOCKS - 1);
+ func(&map->tsan_bucket_locks[lock_idx]);
+ }
+#else
+ func(&b->lock);
+#endif
+}
+
+static inline void qht_bucket_lock_init(const struct qht_map *map,
+ struct qht_bucket *b)
+{
+ qht_do_if_first_in_stripe(map, b, qemu_spin_init);
+}
+
+static inline void qht_bucket_lock_destroy(const struct qht_map *map,
+ struct qht_bucket *b)
+{
+ qht_do_if_first_in_stripe(map, b, (void (*)(QemuSpin *))qemu_spin_destroy);
+}
+
+static inline void qht_bucket_lock_do(const struct qht_map *map,
+ struct qht_bucket *b,
+ void (*func)(QemuSpin *lock))
+{
+#ifdef CONFIG_TSAN
+ unsigned long bucket_idx = b - map->buckets;
+ unsigned long lock_idx = bucket_idx & (QHT_TSAN_BUCKET_LOCKS - 1);
+ func(&map->tsan_bucket_locks[lock_idx]);
+#else
+ func(&b->lock);
+#endif
+}
+
+static inline void qht_bucket_lock(const struct qht_map *map,
+ struct qht_bucket *b)
+{
+ qht_bucket_lock_do(map, b, qemu_spin_lock);
+}
+
+static inline void qht_bucket_unlock(const struct qht_map *map,
+ struct qht_bucket *b)
+{
+ qht_bucket_lock_do(map, b, qemu_spin_unlock);
+}
+
+static inline void qht_head_init(struct qht_map *map, struct qht_bucket *b)
{
memset(b, 0, sizeof(*b));
- qemu_spin_init(&b->lock);
+ qht_bucket_lock_init(map, b);
seqlock_init(&b->sequence);
}
@@ -250,7 +328,7 @@ static void qht_map_lock_buckets(struct qht_map *map)
for (i = 0; i < map->n_buckets; i++) {
struct qht_bucket *b = &map->buckets[i];
- qemu_spin_lock(&b->lock);
+ qht_do_if_first_in_stripe(map, b, qemu_spin_lock);
}
}
@@ -261,7 +339,7 @@ static void qht_map_unlock_buckets(struct qht_map *map)
for (i = 0; i < map->n_buckets; i++) {
struct qht_bucket *b = &map->buckets[i];
- qemu_spin_unlock(&b->lock);
+ qht_do_if_first_in_stripe(map, b, qemu_spin_unlock);
}
}
@@ -308,7 +386,7 @@ void qht_map_lock_buckets__no_stale(struct qht *ht, struct qht_map **pmap)
* Get a head bucket and lock it, making sure its parent map is not stale.
* @pmap is filled with a pointer to the bucket's parent map.
*
- * Unlock with qemu_spin_unlock(&b->lock).
+ * Unlock with qht_bucket_unlock.
*
* Note: callers cannot have ht->lock held.
*/
@@ -322,18 +400,18 @@ struct qht_bucket *qht_bucket_lock__no_stale(struct qht *ht, uint32_t hash,
map = qatomic_rcu_read(&ht->map);
b = qht_map_to_bucket(map, hash);
- qemu_spin_lock(&b->lock);
+ qht_bucket_lock(map, b);
if (likely(!qht_map_is_stale__locked(ht, map))) {
*pmap = map;
return b;
}
- qemu_spin_unlock(&b->lock);
+ qht_bucket_unlock(map, b);
/* we raced with a resize; acquire ht->lock to see the updated ht->map */
qht_lock(ht);
map = ht->map;
b = qht_map_to_bucket(map, hash);
- qemu_spin_lock(&b->lock);
+ qht_bucket_lock(map, b);
qht_unlock(ht);
*pmap = map;
return b;
@@ -345,12 +423,13 @@ static inline bool qht_map_needs_resize(const struct qht_map *map)
map->n_added_buckets_threshold;
}
-static inline void qht_chain_destroy(const struct qht_bucket *head)
+static inline void qht_chain_destroy(const struct qht_map *map,
+ struct qht_bucket *head)
{
struct qht_bucket *curr = head->next;
struct qht_bucket *prev;
- qemu_spin_destroy(&head->lock);
+ qht_bucket_lock_destroy(map, head);
while (curr) {
prev = curr;
curr = curr->next;
@@ -364,7 +443,7 @@ static void qht_map_destroy(struct qht_map *map)
size_t i;
for (i = 0; i < map->n_buckets; i++) {
- qht_chain_destroy(&map->buckets[i]);
+ qht_chain_destroy(map, &map->buckets[i]);
}
qemu_vfree(map->buckets);
g_free(map);
@@ -390,7 +469,7 @@ static struct qht_map *qht_map_create(size_t n_buckets)
map->buckets = qemu_memalign(QHT_BUCKET_ALIGN,
sizeof(*map->buckets) * n_buckets);
for (i = 0; i < n_buckets; i++) {
- qht_head_init(&map->buckets[i]);
+ qht_head_init(map, &map->buckets[i]);
}
return map;
}
@@ -638,7 +717,7 @@ bool qht_insert(struct qht *ht, void *p, uint32_t hash, void **existing)
b = qht_bucket_lock__no_stale(ht, hash, &map);
prev = qht_insert__locked(ht, map, b, p, hash, &needs_resize);
qht_bucket_debug__locked(b);
- qemu_spin_unlock(&b->lock);
+ qht_bucket_unlock(map, b);
if (unlikely(needs_resize) && ht->mode & QHT_MODE_AUTO_RESIZE) {
qht_grow_maybe(ht);
@@ -749,7 +828,7 @@ bool qht_remove(struct qht *ht, const void *p, uint32_t hash)
b = qht_bucket_lock__no_stale(ht, hash, &map);
ret = qht_remove__locked(b, p, hash);
qht_bucket_debug__locked(b);
- qemu_spin_unlock(&b->lock);
+ qht_bucket_unlock(map, b);
return ret;
}
Fixes this tsan crash, easy to reproduce with any large enough program: $ tests/unit/test-qht 1..2 ThreadSanitizer: CHECK failed: sanitizer_deadlock_detector.h:67 "((n_all_locks_)) < (((sizeof(all_locks_with_contexts_)/sizeof((all_locks_with_contexts_)[0]))))" (0x40, 0x40) (tid=1821568) #0 __tsan::CheckUnwind() ../../../../src/libsanitizer/tsan/tsan_rtl.cpp:353 (libtsan.so.2+0x90034) #1 __sanitizer::CheckFailed(char const*, int, char const*, unsigned long long, unsigned long long) ../../../../src/libsanitizer/sanitizer_common/sanitizer_termination.cpp:86 (libtsan.so.2+0xca555) #2 __sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::addLock(unsigned long, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:67 (libtsan.so.2+0xb3616) #3 __sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::addLock(unsigned long, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:59 (libtsan.so.2+0xb3616) #4 __sanitizer::DeadlockDetector<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >::onLockAfter(__sanitizer::DeadlockDetectorTLS<__sanitizer::TwoLevelBitVector<1ul, __sanitizer::BasicBitVector<unsigned long> > >*, unsigned long, unsigned int) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector.h:216 (libtsan.so.2+0xb3616) #5 __sanitizer::DD::MutexAfterLock(__sanitizer::DDCallback*, __sanitizer::DDMutex*, bool, bool) ../../../../src/libsanitizer/sanitizer_common/sanitizer_deadlock_detector1.cpp:169 (libtsan.so.2+0xb3616) #6 __tsan::MutexPostLock(__tsan::ThreadState*, unsigned long, unsigned long, unsigned int, int) ../../../../src/libsanitizer/tsan/tsan_rtl_mutex.cpp:200 (libtsan.so.2+0xa3382) #7 __tsan_mutex_post_lock ../../../../src/libsanitizer/tsan/tsan_interface_ann.cpp:384 (libtsan.so.2+0x76bc3) #8 qemu_spin_lock /home/cota/src/qemu/include/qemu/thread.h:259 (test-qht+0x44a97) #9 qht_map_lock_buckets ../util/qht.c:253 (test-qht+0x44a97) #10 do_qht_iter ../util/qht.c:809 (test-qht+0x45f33) #11 qht_iter ../util/qht.c:821 (test-qht+0x45f33) #12 iter_check ../tests/unit/test-qht.c:121 (test-qht+0xe473) #13 qht_do_test ../tests/unit/test-qht.c:202 (test-qht+0xe473) #14 qht_test ../tests/unit/test-qht.c:240 (test-qht+0xe7c1) #15 test_default ../tests/unit/test-qht.c:246 (test-qht+0xe828) #16 <null> <null> (libglib-2.0.so.0+0x7daed) #17 <null> <null> (libglib-2.0.so.0+0x7d80a) #18 <null> <null> (libglib-2.0.so.0+0x7d80a) #19 g_test_run_suite <null> (libglib-2.0.so.0+0x7dfe9) #20 g_test_run <null> (libglib-2.0.so.0+0x7e055) #21 main ../tests/unit/test-qht.c:259 (test-qht+0xd2c6) #22 __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 (libc.so.6+0x29d8f) #23 __libc_start_main_impl ../csu/libc-start.c:392 (libc.so.6+0x29e3f) #24 _start <null> (test-qht+0xdb44) Signed-off-by: Emilio Cota <cota@braap.org> --- util/qht.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 93 insertions(+), 14 deletions(-)