From: Fengnan Chang Date: Wed, 13 Aug 2025 12:02:14 +0000 (+0800) Subject: io_uring/io-wq: add check free worker before create new worker X-Git-Tag: io_uring-6.17-20250815 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=90bf5aab4674c9cca1073d5b5fd539c39e3c96be;p=linux-block.git io_uring/io-wq: add check free worker before create new worker After commit 0b2b066f8a85 ("io_uring/io-wq: only create a new worker if it can make progress"), in our produce environment, we still observe that part of io_worker threads keeps creating and destroying. After analysis, it was confirmed that this was due to a more complex scenario involving a large number of fsync operations, which can be abstracted as frequent write + fsync operations on multiple files in a single uring instance. Since write is a hash operation while fsync is not, and fsync is likely to be suspended during execution, the action of checking the hash value in io_wqe_dec_running cannot handle such scenarios. Similarly, if hash-based work and non-hash-based work are sent at the same time, similar issues are likely to occur. Returning to the starting point of the issue, when a new work arrives, io_wq_enqueue may wake up free worker A, while io_wq_dec_running may create worker B. Ultimately, only one of A and B can obtain and process the task, leaving the other in an idle state. In the end, the issue is caused by inconsistent logic in the checks performed by io_wq_enqueue and io_wq_dec_running. Therefore, the problem can be resolved by checking for available workers in io_wq_dec_running. Signed-off-by: Fengnan Chang Reviewed-by: Diangang Li Link: https://lore.kernel.org/r/20250813120214.18729-1-changfengnan@bytedance.com Signed-off-by: Jens Axboe --- diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index be91edf34f01..17dfaa0395c4 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -357,6 +357,13 @@ static void create_worker_cb(struct callback_head *cb) worker = container_of(cb, struct io_worker, create_work); wq = worker->wq; acct = worker->acct; + + rcu_read_lock(); + do_create = !io_acct_activate_free_worker(acct); + rcu_read_unlock(); + if (!do_create) + goto no_need_create; + raw_spin_lock(&acct->workers_lock); if (acct->nr_workers < acct->max_workers) { @@ -367,6 +374,7 @@ static void create_worker_cb(struct callback_head *cb) if (do_create) { create_io_worker(wq, acct); } else { +no_need_create: atomic_dec(&acct->nr_running); io_worker_ref_put(wq); }