From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793209714; b=Q4c7CgVu9FwmckXGEBAWu10NKHIUSmb4O/zhsbZep2VFCbMeR5EfLGQCwrf/C0buWxnZ HJGI2HTo4iOeudB+zCYudyYpsRu90wM0KjbwmItakQ69fT8DkhQZmqEKCR06K+xUju9qh WUvA/hPPIkgmOU6x1vsG/G7SKc4HdehS3EbQy52NTGQ8InbOFaCL9Pdqub2TSEauNgWEp OiYTxIMRyTue9bLq2oZ1FKiGteYjIuUK1y7XuZ4qX9Mat6F4YGpNXl5fUk8nhFaMKcEvb QfOSWYQq0TihaEltTDS8EK26gsOagxueI1hXfXa/8Ko8VVsII0syVXYyMpQnydVc5mA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793209714; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=vGk+DQaP1FMQyuVL7v0txZ4gkvT6GwiTE7YzMD7YteA=; b=JeCxbvZay/vGlZm1NHVRVaeqoHENOI8PORIxgFfsS5HkDNHCZnkH69RsPJIt1qAJ+PFg lPmpsOT4GqU1TVjpoawrhtkuv8CD78hgZPszaO7Vs979AoSmY2mOPQlbDRTzSdRy5Req9 04ftjDSqptoMu+FaJkAi/PK4OeypJ351y26FTGuo2xVn4UdGZ379cpdoE6RG/f21CMKpf 8MdJj+CO6rxSz1oVzvkL2tOsC9oln0XaypFXtzpnpO+yllCL6dQ0o/BuG+zQ/SnfGWKvJ ZFlTvOugzvvWTyuLISq6lynteeEKf4pi/pb2E+kSmJx99BzY+h2DeoHy+bmeKIX2sjg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=nl5ZU2TA; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 38F7A606A31A; Wed, 28 Oct 2026 17:48:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=nl5ZU2TA Received: by smtp.kernel.org (Postfix) with ESMTPSA id 479AE1F01825; Wed, 28 Oct 2026 17:48:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793209713; bh=vGk+DQaP1FMQyuVL7v0txZ4gkvT6GwiTE7YzMD7YteA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=nl5ZU2TAOSW4N7r1wSzkQN6aBerd2oZ2hMJ4eqAftAy4uLsNXrx8VzQmOgYWNO5xe ZLhOJ7icTmdq/cz209rD52NrsQLY6/h+fVbUifzoprN+ioGU+56Z8FTjGf9f5N5RUT uUusgcfLwU8wtChgAG4QAfr8P0sk9Qkmst3Y0mqI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Josef Bacik , Jens Axboe Subject: [PATCH 6.18 052/109] io_uring/io-wq: dont exit with a creation pending Date: Wed, 28 Oct 2026 18:00:36 +0100 Message-ID: <20261028165943.585404886@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028165942.357251485@linuxfoundation.org> References: <20261028165942.357251485@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josef Bacik Commit e231d2e8f80d3649ecd3851b7f2abdfbe606c04b upstream. A worker that is the last one to go to sleep while work is pending asks for another worker. io_wq_dec_running() bumps ->nr_running on behalf of the new worker and queues create_worker_cb() as task_work for the owner of the io-wq. Until that has run, everybody else takes it that a worker is running which is going to look after the work list: io_wq_enqueue() doesn't create one, and other workers that go to sleep don't find themselves to be the last. If the worker that made the request exits, io_worker_exit() cancels the task_work, and io_worker_cancel_cb() drops ->nr_running without a look at the work list: worker A worker B io_wq_enqueue() blocks, work is pending nr_running++ queues create_worker_cb() wakes, handles the work idle timeout, decides to exit picks up work 1 queues work 2 B is on the free list still: wakes B work 1 blocks nr_running 2 -> 1 io_worker_exit() io_worker_cancel_cb() nr_running 1 -> 0 Work 2 has to wait for work 1, although there is room for more workers. It takes an owner that doesn't get around to run its task_work for the time of the idle timeout, less if the worker exits because its affinity was changed or the io-wq is marked exit-on-idle. Let the worker stay around until its request has been dealt with. Only the worker itself sets ->create_state, so it can't be set behind its back once it has decided to leave. Fixes: 1d5f5ea7cb7d ("io-wq: remove worker to owner tw dependency") Assisted-by: LLM Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-12-c1556f5d7bf5@toxicpanda.com Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- io_uring/io-wq.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -755,9 +755,13 @@ static int io_wq_worker(void *data) * idle-exit, drop the worker as well. This is used to avoid * keeping io-wq workers around for tasks that no longer have * any active io_uring instances. + * Not as long as a request of ours for another worker is + * pending, though. It is accounted as a running worker, which + * others rely on, and io_worker_exit() would cancel it. */ - if ((last_timeout && (exit_mask || acct->nr_workers > 1)) || - test_bit(IO_WQ_BIT_EXIT_ON_IDLE, &wq->state)) { + if (((last_timeout && (exit_mask || acct->nr_workers > 1)) || + test_bit(IO_WQ_BIT_EXIT_ON_IDLE, &wq->state)) && + !test_bit(0, &worker->create_state)) { acct->nr_workers--; if (test_and_clear_bit(IO_WORKER_F_FREE, &worker->flags)) hlist_nulls_del_init_rcu(&worker->nulls_node);