From: Yu Kuai <yukuai1@huaweicloud.com>
To: axboe@kernel.dk, asml.silence@gmail.com, osandov@fb.com, jack@suse.cz
Cc: kbusch@kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org, yukuai3@huawei.com,
yukuai1@huaweicloud.com, yi.zhang@huawei.com
Subject: [PATCH RFC v3 1/3] sbitmap: fix that same waitqueue can be woken up continuously
Date: Sun, 10 Jul 2022 12:21:58 +0800 [thread overview]
Message-ID: <20220710042200.20936-2-yukuai1@huaweicloud.com> (raw)
In-Reply-To: <20220710042200.20936-1-yukuai1@huaweicloud.com>
From: Yu Kuai <yukuai3@huawei.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@huawei.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
next prev parent reply other threads:[~2022-07-10 4:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-10 4:21 [PATCH RFC v3 0/3] bugfix for sbitmap Yu Kuai
2022-07-10 4:21 ` Yu Kuai [this message]
2022-07-11 14:20 ` [PATCH RFC v3 1/3] sbitmap: fix that same waitqueue can be woken up continuously Jan Kara
2022-07-12 13:25 ` Yu Kuai
2022-07-10 4:21 ` [PATCH RFC v3 2/3] sbitmap: fix invalid wakeup on the wrong waitqueue Yu Kuai
2022-07-11 14:26 ` Jan Kara
2022-07-12 13:26 ` Yu Kuai
2022-07-10 4:22 ` [PATCH RFC v3 3/3] sbitmap: fix that 'wait_cnt' can be decreased while waitqueue is empty Yu Kuai
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20220710042200.20936-2-yukuai1@huaweicloud.com \
--to=yukuai1@huaweicloud.com \
--cc=asml.silence@gmail.com \
--cc=axboe@kernel.dk \
--cc=jack@suse.cz \
--cc=kbusch@kernel.org \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=osandov@fb.com \
--cc=yi.zhang@huawei.com \
--cc=yukuai3@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.