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authorKeith Busch <kbusch@kernel.org>2022-09-09 11:40:22 -0700
committerJens Axboe <axboe@kernel.dk>2022-09-12 00:10:34 -0600
commit4acb83417cadfdcbe64215f9d0ddcf3132af808e (patch)
tree45bdd14acf29ddc9b49cbb26e30323446d4aaeb6
parentc35227d4e8cbc70a6622cc7cc5f8c3bff513f1fa (diff)
sbitmap: fix batched wait_cnt accounting
Batched completions can clear multiple bits, but we're only decrementing the wait_cnt by one each time. This can cause waiters to never be woken, stalling IO. Use the batched count instead. Link: https://bugzilla.kernel.org/show_bug.cgi?id=215679 Signed-off-by: Keith Busch <kbusch@kernel.org> Link: https://lore.kernel.org/r/20220909184022.1709476-1-kbusch@fb.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/blk-mq-tag.c2
-rw-r--r--include/linux/sbitmap.h3
-rw-r--r--lib/sbitmap.c37
3 files changed, 26 insertions, 16 deletions
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 8e3b36d1cb57..9eb968e14d31 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -196,7 +196,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
* other allocations on previous queue won't be starved.
*/
if (bt != bt_prev)
- sbitmap_queue_wake_up(bt_prev);
+ sbitmap_queue_wake_up(bt_prev, 1);
ws = bt_wait_ptr(bt, data->hctx);
} while (1);
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 8f5a86e210b9..4d2d5205ab58 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -575,8 +575,9 @@ void sbitmap_queue_wake_all(struct sbitmap_queue *sbq);
* sbitmap_queue_wake_up() - Wake up some of waiters in one waitqueue
* on a &struct sbitmap_queue.
* @sbq: Bitmap queue to wake up.
+ * @nr: Number of bits cleared.
*/
-void sbitmap_queue_wake_up(struct sbitmap_queue *sbq);
+void sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr);
/**
* sbitmap_queue_show() - Dump &struct sbitmap_queue information to a &struct
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index cbfd2e677d87..624fa7f118d1 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -599,24 +599,31 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
return NULL;
}
-static bool __sbq_wake_up(struct sbitmap_queue *sbq)
+static bool __sbq_wake_up(struct sbitmap_queue *sbq, int *nr)
{
struct sbq_wait_state *ws;
unsigned int wake_batch;
- int wait_cnt;
+ int wait_cnt, cur, sub;
bool ret;
+ if (*nr <= 0)
+ return false;
+
ws = sbq_wake_ptr(sbq);
if (!ws)
return false;
- wait_cnt = atomic_dec_return(&ws->wait_cnt);
- /*
- * 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;
+ cur = atomic_read(&ws->wait_cnt);
+ do {
+ /*
+ * For concurrent callers of this, callers should call this
+ * function again to wakeup a new batch on a different 'ws'.
+ */
+ if (cur == 0)
+ return true;
+ sub = min(*nr, cur);
+ wait_cnt = cur - sub;
+ } while (!atomic_try_cmpxchg(&ws->wait_cnt, &cur, wait_cnt));
/*
* If we decremented queue without waiters, retry to avoid lost
@@ -625,6 +632,8 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
if (wait_cnt > 0)
return !waitqueue_active(&ws->wait);
+ *nr -= sub;
+
/*
* When wait_cnt == 0, we have to be particularly careful as we are
* responsible to reset wait_cnt regardless whether we've actually
@@ -660,12 +669,12 @@ static bool __sbq_wake_up(struct sbitmap_queue *sbq)
sbq_index_atomic_inc(&sbq->wake_index);
atomic_set(&ws->wait_cnt, wake_batch);
- return ret;
+ return ret || *nr;
}
-void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
+void sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr)
{
- while (__sbq_wake_up(sbq))
+ while (__sbq_wake_up(sbq, &nr))
;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
@@ -705,7 +714,7 @@ void sbitmap_queue_clear_batch(struct sbitmap_queue *sbq, int offset,
atomic_long_andnot(mask, (atomic_long_t *) addr);
smp_mb__after_atomic();
- sbitmap_queue_wake_up(sbq);
+ sbitmap_queue_wake_up(sbq, nr_tags);
sbitmap_update_cpu_hint(&sbq->sb, raw_smp_processor_id(),
tags[nr_tags - 1] - offset);
}
@@ -733,7 +742,7 @@ void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
* waiter. See the comment on waitqueue_active().
*/
smp_mb__after_atomic();
- sbitmap_queue_wake_up(sbq);
+ sbitmap_queue_wake_up(sbq, 1);
sbitmap_update_cpu_hint(&sbq->sb, cpu, nr);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_clear);