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=1793209711; b=yNuHZS+KDb6v/uh20ZeM1FpMitoAEKaVqcWYemhh4RGqUJv7AN8RmjIppfk3kplH7l9Y H2+Ej9cd1luuvgI2xUkS45ePdDVFkCNI/bE7wisbkmiRzT39YeLL7sFFAazpSuIK3QaNB kiOjlUYbX4+J+Wu7qi0eMUTb7l49Oue1oU+RPP5Nq/AdkWjWZj2WjTQbrq0aXxLoh27NS x9+z5NjzXhJwr7s0gKhz/IzmWpCPYbAZzzwhEzN7ulZaBc+CGw+2cgnbGZ2e1c74p8TEd mYndmyrKct0MBb2L7SjoFV31A6e7TqlT5yVoSdOIglAWkf8k9S2WRFf0TnvcNlEwWqw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793209711; 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=Uzhigpqa1rwyRgjTSNBKKqAxkZBipT0wVnpHP6grQB4=; b=3hpv891eR2LH/vY5VZjbCy3frsnQLsvTRNZ5lOGCRodQDJ4ESDKz1cBrBBC4maRkl3nS mBrTEL81DRaaR26jRDqRCQE78tJZWna0oIW53URrJqf/xsUZc/VfI5ExUiFalOfFW0XCL lqTiQfxVTWAFaztaOaeTrZHNxM1l7l90nvMnku7Kh/+jpkTnWRNp2Cn0nMTV3u78UktI6 JJ+fFc0aSHp0KByu4zSEyCNyt5XFOYq/eQkINi+PB9F486YlzMIszu/+7sZwOC+jljXip vvKLh2PexxJFHE38KDFZAbKAL3eVAHFw5btlIiP/KOi7AGiGMVCk06ug6mh/nMRfs3w== 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=sa4DbkgM; 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 51315606A31D; Wed, 28 Oct 2026 17:48:31 +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=sa4DbkgM Received: by smtp.kernel.org (Postfix) with ESMTPSA id 636911F01825; Wed, 28 Oct 2026 17:48:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793209710; bh=Uzhigpqa1rwyRgjTSNBKKqAxkZBipT0wVnpHP6grQB4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=sa4DbkgMpBDSDfQm8jrlLHNsFWH4eugs9IGAE9WRe6MS3EuVnNFbFSw4zPuXLinlW 4lKqSNqLJL2+/VA11UQEfP0nRKS0xYNkNr6RN2b+ZzTzMaP695hK2eLD4R3hKfU8DO dPX9sRyU8Hmn3f/uS6nHDOex+zZSeWxQQpHYwxxo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Josef Bacik , Jens Axboe Subject: [PATCH 6.18 051/109] io_uring/io-wq: dont strand work when a worker exits Date: Wed, 28 Oct 2026 18:00:35 +0100 Message-ID: <20261028165943.562305427@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 ad41f325be1271b22d99353819c90f0d5e45acc8 upstream. A worker exits if its idle timeout fired and it isn't the last one, if its affinity was changed, or if the wq is marked exit-on-idle. It decides so after it found the work list empty, and until io_worker_exit() is through it stays on the free list and in ->nr_running: worker io_wq_enqueue() io_acct_run_queue() == false queues work io_acct_activate_free_worker() wake_up_process(worker) // found one, nothing to create acct->nr_workers-- break io_worker_exit() Nobody is going to look at the work. If other workers exist, it has to wait until one of them finishes what it is blocked on or hits its idle timeout. If not, which is possible for the affinity and the exit-on-idle case, it sits there until something else is queued. For exit-on-idle it takes a task that closes its last ring and sets up a new one while the workers are on their way out. Make the worker take itself off the free list when it gives up its ->nr_workers slot, then leave ->nr_running, and only then take the final look at the work list. That look and queueing work are both done under acct->lock, so either the worker sees the work and stays, or the enqueue side sees that the worker is gone and wakes or creates another one. If it wants to stay and finds that its slot has been taken, a worker has been created in its place, which is going to look at the work list, and it can leave after all. Fixes: 38aa434ab933 ("io_uring/io-wq: add exit-on-idle state") Fixes: 05c5f4ee4da7 ("io-wq: get rid of FIXED worker flag") Assisted-by: LLM Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-11-c1556f5d7bf5@toxicpanda.com Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- io_uring/io-wq.c | 36 +++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -693,6 +693,35 @@ static void io_worker_handle_work(struct } while (1); } +/* + * The worker has decided to exit, and has given up its ->nr_workers slot and + * its place on the free list. io_wq_enqueue() may have picked it from that + * list, or seen it running, after it last looked at the work list. Leave + * ->nr_running as well and check again. Returns false if the worker has to + * stay. + */ +static bool io_worker_retire(struct io_wq_acct *acct, struct io_worker *worker) +{ + /* turns io_wq_dec_running() and the scheduler hooks into no-ops */ + clear_bit(IO_WORKER_F_UP, &worker->flags); + atomic_dec(&acct->nr_running); + if (!io_acct_run_queue(acct)) + return true; + raw_spin_unlock(&acct->lock); + + raw_spin_lock(&acct->workers_lock); + if (acct->nr_workers >= acct->max_workers) { + /* a worker was created in our place, the work is its business */ + raw_spin_unlock(&acct->workers_lock); + return true; + } + acct->nr_workers++; + raw_spin_unlock(&acct->workers_lock); + atomic_inc(&acct->nr_running); + set_bit(IO_WORKER_F_UP, &worker->flags); + return false; +} + static int io_wq_worker(void *data) { struct io_worker *worker = data; @@ -730,9 +759,14 @@ static int io_wq_worker(void *data) if ((last_timeout && (exit_mask || acct->nr_workers > 1)) || test_bit(IO_WQ_BIT_EXIT_ON_IDLE, &wq->state)) { acct->nr_workers--; + if (test_and_clear_bit(IO_WORKER_F_FREE, &worker->flags)) + hlist_nulls_del_init_rcu(&worker->nulls_node); raw_spin_unlock(&acct->workers_lock); __set_current_state(TASK_RUNNING); - break; + if (io_worker_retire(acct, worker)) + break; + last_timeout = false; + continue; } last_timeout = false; __io_worker_idle(acct, worker);