[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20220710042200.20936-2-yukuai1@huaweicloud.com>
Date: Sun, 10 Jul 2022 12:21:58 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk, asml.silence@...il.com, osandov@...com,
jack@...e.cz
Cc: kbusch@...nel.org, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, yukuai3@...wei.com,
yukuai1@...weicloud.com, yi.zhang@...wei.com
Subject: [PATCH RFC v3 1/3] sbitmap: fix that same waitqueue can be woken up continuously
From: Yu Kuai <yukuai3@...wei.com>
__sbq_wake_up __sbq_wake_up
sbq_wake_ptr -> assume 0
sbq_wake_ptr -> 0
atomic_dec_return
atomic_dec_return
atomic_cmpxchg -> succeed
atomic_cmpxchg -> failed
return true
__sbq_wake_up
sbq_wake_ptr
atomic_read(&sbq->wake_index) -> still 0
sbq_index_atomic_inc -> inc to 1
if (waitqueue_active(&ws->wait))
if (wake_index != atomic_read(&sbq->wake_index))
atomic_set -> reset from 1 to 0
wake_up_nr -> wake up first waitqueue
// continue to wake up in first waitqueue
Fix the problem by using atomic_cmpxchg() instead of atomic_set()
to update 'wake_index'.
Fixes: 417232880c8a ("sbitmap: Replace cmpxchg with xchg")
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
lib/sbitmap.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 29eb0484215a..b46fce1beb3a 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -579,19 +579,24 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);
static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
{
- int i, wake_index;
+ int i, wake_index, old_wake_index;
+again:
if (!atomic_read(&sbq->ws_active))
return NULL;
- wake_index = atomic_read(&sbq->wake_index);
+ old_wake_index = wake_index = atomic_read(&sbq->wake_index);
for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
struct sbq_wait_state *ws = &sbq->ws[wake_index];
if (waitqueue_active(&ws->wait)) {
- if (wake_index != atomic_read(&sbq->wake_index))
- atomic_set(&sbq->wake_index, wake_index);
- return ws;
+ if (wake_index == old_wake_index)
+ return ws;
+
+ if (atomic_cmpxchg(&sbq->wake_index, old_wake_index,
+ wake_index) == old_wake_index)
+ return ws;
+ goto again;
}
wake_index = sbq_index_inc(wake_index);
--
2.31.1
Powered by blists - more mailing lists