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* [PATCH 5.15] io-wq: max_worker fixes
@ 2021-10-19 19:31 Pavel Begunkov
  2021-10-19 19:41 ` Jens Axboe
  2021-10-19 22:54 ` Pavel Begunkov
  0 siblings, 2 replies; 4+ messages in thread
From: Pavel Begunkov @ 2021-10-19 19:31 UTC (permalink / raw)
  To: io-uring; +Cc: Jens Axboe, asml.silence

First, fix nr_workers checks against max_workers, with max_worker
registration, it may pretty easily happen that nr_workers > max_workers.

Also, synchronise writing to acct->max_worker with wqe->lock. It's not
an actual problem, but as we don't care about io_wqe_create_worker(),
it's better than WRITE_ONCE()/READ_ONCE().

Fixes: 2e480058ddc2 ("io-wq: provide a way to limit max number of workers")
Signed-off-by: Pavel Begunkov <[email protected]>
---
 fs/io-wq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 811299ac9684..cdf1719f6be6 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -253,7 +253,7 @@ static bool io_wqe_create_worker(struct io_wqe *wqe, struct io_wqe_acct *acct)
 		pr_warn_once("io-wq is not configured for unbound workers");
 
 	raw_spin_lock(&wqe->lock);
-	if (acct->nr_workers == acct->max_workers) {
+	if (acct->nr_workers >= acct->max_workers) {
 		raw_spin_unlock(&wqe->lock);
 		return true;
 	}
@@ -1290,15 +1290,18 @@ int io_wq_max_workers(struct io_wq *wq, int *new_count)
 
 	rcu_read_lock();
 	for_each_node(node) {
+		struct io_wqe *wqe = wq->wqes[node];
 		struct io_wqe_acct *acct;
 
+		raw_spin_lock(&wqe->lock);
 		for (i = 0; i < IO_WQ_ACCT_NR; i++) {
-			acct = &wq->wqes[node]->acct[i];
+			acct = &wqe->acct[i];
 			prev = max_t(int, acct->max_workers, prev);
 			if (new_count[i])
 				acct->max_workers = new_count[i];
 			new_count[i] = prev;
 		}
+		raw_spin_unlock(&wqe->lock);
 	}
 	rcu_read_unlock();
 	return 0;
-- 
2.33.0


^ permalink raw reply related	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2021-10-19 23:09 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2021-10-19 19:31 [PATCH 5.15] io-wq: max_worker fixes Pavel Begunkov
2021-10-19 19:41 ` Jens Axboe
2021-10-19 22:54 ` Pavel Begunkov
2021-10-19 23:09   ` Jens Axboe

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