Re: [PATCH] io_uring/io-wq: add check free worker before create new worker

[Jens Axboe <axboe@kernel.dk>]

On Wed, 13 Aug 2025 20:02:14 +0800, Fengnan Chang wrote:
> 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.
> 
> [...]

Applied, thanks!

[1/1] io_uring/io-wq: add check free worker before create new worker
      commit: 9d83e1f05c98bab5de350bef89177e2be8b34db0

Best regards,
-- 
Jens Axboe