@@ -615,34 +615,31 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
return false;
wait_cnt = atomic_dec_return(&ws->wait_cnt);
- if (wait_cnt <= 0) {
- int ret;
+ if (wait_cnt > 0)
+ return false;
- wake_batch = READ_ONCE(sbq->wake_batch);
+ /*
+ * For concurrent callers of this, callers should call this function
+ * again to wakeup a new batch on a different 'ws'.
+ */
+ if (wait_cnt < 0)
+ return true;
- /*
- * Pairs with the memory barrier in sbitmap_queue_resize() to
- * ensure that we see the batch size update before the wait
- * count is reset.
- */
- smp_mb__before_atomic();
+ wake_batch = READ_ONCE(sbq->wake_batch);
- /*
- * For concurrent callers of this, the one that failed the
- * atomic_cmpxhcg() race should call this function again
- * to wakeup a new batch on a different 'ws'.
- */
- ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
- if (ret == wait_cnt) {
- sbq_index_atomic_inc(&sbq->wake_index);
- wake_up_nr(&ws->wait, wake_batch);
- return false;
- }
+ /*
+ * Pairs with the memory barrier in sbitmap_queue_resize() to
+ * ensure that we see the batch size update before the wait
+ * count is reset.
+ */
+ smp_mb__before_atomic();
- return true;
- }
+ /* increase wake_index first to prevent possible lost wakeups */
+ sbq_index_atomic_inc(&sbq->wake_index);
+ atomic_set(&ws->wait_cnt, wake_batch);
+ wake_up_nr(&ws->wait, wake_batch);
- return false;
+ return true;
}
void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
For example, 2 * wake_batch tags are put, while only wake_batch threads are woken: __sbq_wake_up atomic_cmpxchg -> reset wait_cnt __sbq_wake_up -> decrease wait_cnt ... __sbq_wake_up -> wait_cnt is decreased to 0 again atomic_cmpxchg sbq_index_atomic_inc -> increase wake_index wake_up_nr -> wake up and waitqueue might be empty sbq_index_atomic_inc -> increase again, one waitqueue is skipped wake_up_nr -> invalid wake up because old wakequeue might be empty To fix the problem, increasing 'wake_index' before resetting 'wait_cnt'. Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library") Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- lib/sbitmap.c | 43 ++++++++++++++++++++----------------------- 1 file changed, 20 insertions(+), 23 deletions(-)