6.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: David Jeffery djeffery@redhat.com
commit 106397376c0369fcc01c58dd189ff925a2724a57 upstream.
Current code supposes that it is enough to provide forward progress by just waking up one wait queue after one completion batch is done.
Unfortunately this way isn't enough, cause waiter can be added to wait queue just after it is woken up.
Follows one example(64 depth, wake_batch is 8)
1) all 64 tags are active
2) in each wait queue, there is only one single waiter
3) each time one completion batch(8 completions) wakes up just one waiter in each wait queue, then immediately one new sleeper is added to this wait queue
4) after 64 completions, 8 waiters are wakeup, and there are still 8 waiters in each wait queue
5) after another 8 active tags are completed, only one waiter can be wakeup, and the other 7 can't be waken up anymore.
Turns out it isn't easy to fix this problem, so simply wakeup enough waiters for single batch.
Cc: Kemeng Shi shikemeng@huaweicloud.com Cc: Chengming Zhou zhouchengming@bytedance.com Cc: Jan Kara jack@suse.cz Signed-off-by: David Jeffery djeffery@redhat.com Signed-off-by: Ming Lei ming.lei@redhat.com Reviewed-by: Gabriel Krisman Bertazi krisman@suse.de Reviewed-by: Keith Busch kbusch@kernel.org Link: https://lore.kernel.org/r/20230721095715.232728-1-ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- lib/sbitmap.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-)
--- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -550,7 +550,7 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_min_shal
static void __sbitmap_queue_wake_up(struct sbitmap_queue *sbq, int nr) { - int i, wake_index; + int i, wake_index, woken;
if (!atomic_read(&sbq->ws_active)) return; @@ -567,13 +567,12 @@ static void __sbitmap_queue_wake_up(stru */ wake_index = sbq_index_inc(wake_index);
- /* - * It is sufficient to wake up at least one waiter to - * guarantee forward progress. - */ - if (waitqueue_active(&ws->wait) && - wake_up_nr(&ws->wait, nr)) - break; + if (waitqueue_active(&ws->wait)) { + woken = wake_up_nr(&ws->wait, nr); + if (woken == nr) + break; + nr -= woken; + } }
if (wake_index != atomic_read(&sbq->wake_index))