This is a note to let you know that I've just added the patch titled
sbitmap: fix batching wakeup
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sbitmap-fix-batching-wakeup.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 106397376c0369fcc01c58dd189ff925a2724a57 Mon Sep 17 00:00:00 2001
From: David Jeffery <djeffery@xxxxxxxxxx>
Date: Fri, 21 Jul 2023 17:57:15 +0800
Subject: sbitmap: fix batching wakeup
From: David Jeffery <djeffery@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
Reviewed-by: Gabriel Krisman Bertazi <krisman@xxxxxxx>
Reviewed-by: Keith Busch <kbusch@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230721095715.232728-1-ming.lei@xxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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))
Patches currently in stable-queue which might be from djeffery@xxxxxxxxxx are
queue-6.4/sbitmap-fix-batching-wakeup.patch
