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=1793207955; b=dXTq1ESM2OTpQPNRHOGVlJuFjtnhtaFRJvgq/ClMh/1GOASDYPq/C31WKpeG7Q8VOScd CcRzSw8Wgo0PS9MTOtAoR2Iir5js5OR+3Z//DqN5eBws7HyXE7iGngfMOG65vhnVCu6uZ TjTlg/y3D7G+NY7bMfx/LL8nXZddXbPX7GUnes17sV1yHHrrVJaHwHowoE5CUfIY2o9Pr ZYf0NvIi8wP6/TOvLtbilnJzVC7sJIR90JYXC4aL3Sw+eVEMK2EXBeNqhC2te938Nlm6T N3DExy+47N57aFZzGy2tmLFzrGL7t+Ig8pKLcKi0SruwQw3h5bIBErIxlUK8GZiOWkA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793207955; 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=+O0K2O/zm7jqqkQ1+XC8Fc4GbnMbHOlfzQFgom0lBV8=; b=cAQNIDizIW2/WbZABPt5SMETeWNfThavMSrCnQYtPnmCswa8n1xnaxp5F4zCfhyV6go7 3d8rAdT53oTutTCnBWBXIHgBWOPv+hPHk9oVNY6vIaEavR4y7OP2Bhi/HiF1Bv/tqF8zc gDYT5qqXVolskwhMV/oMTDZfp4pMOQc7fniG+JyQ46zLH98VNqrcgQtpmNcGYDK1Kjl2E jSEKBi9YmETufywfSbA3Q3xO8kgycYiUSKHEguUGnPx/5Y2jZWW3SG+vQ1k+CN18k6qfV sSxn13zUUYzWXQv20oHz8lQwjEEJFIvkI/GsgfMqQUcp6885p0eMzONB+U+OnPUszTA== 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=2cnBiSRG; 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 D6066606A325; Wed, 28 Oct 2026 17:19:14 +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=2cnBiSRG Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3054A1F01829; Wed, 28 Oct 2026 17:19:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793207954; bh=+O0K2O/zm7jqqkQ1+XC8Fc4GbnMbHOlfzQFgom0lBV8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=2cnBiSRGrVgLpDh8AwZXiNOnSjPmkvNO554Y0R2PWY8+kaETmby5jyH3iV8MI4XST tYwW9SuuxcFlNky8YNuAeM3SlXQPJUdOMIiWBhSxNssiVQnNkfFIl8FHu02+jcFzVV 85a5JwO0uJN9G/dyEeDlxhg4gohDzUHOOhCCuwnw= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Josef Bacik , Jens Axboe Subject: [PATCH 6.12 198/247] io_uring: dont flood a cancelling task with task_work Date: Wed, 28 Oct 2026 18:00:01 +0100 Message-ID: <20261028165952.108337637@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261028165947.349197979@linuxfoundation.org> References: <20261028165947.349197979@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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Josef Bacik Commit 22e643e61b9b6299b42ff7d88bab48bccada8a5d upstream. io_ring_exit_work() asks each task which has used the ring to remove its tctx node, by task_work, and repeats that until the list is empty. io_tctx_exit_cb() doesn't touch the node while the task is in io_uring_cancel_generic(), which removes all the nodes at its end. So the work item queues the callback again as soon as it has completed, for nothing. That is more than a waste of time. task_work_run() only returns when it finds the list empty. If the rings are released from inside the cancellation, because requests of other rings held the last references to their files, up to 64 work items keep sending callbacks to the one task which is running them. It never finds the list empty, never gets back to the cancellation, the nodes stay, and so it goes on: a task with 60 pairs of rings which poll each other ran 280000 callbacks in 5 seconds, 20 seconds after exit_group(). It ends when all the senders happen to be late at the same time. Until then the task keeps a CPU and the work items busy. An exiting task can't be killed meanwhile. execve() cancels the requests in the same way, so a live task can get stuck there as well, for minutes. If it takes more than five, the work items run into the WARN_ON_ONCE(time_after(jiffies, timeout)) of io_ring_exit_work(). No privilege is needed for any of this. If the callback has met a task in cancellation, wait a little before it is sent again. Nobody has to wake the work item up for that: either the node is gone by then, or it is the turn of the next round. Fixes: d56d938b4bef ("io_uring: do ctx initiated file note removal") Assisted-by: LLM Signed-off-by: Josef Bacik Link: https://patch.msgid.link/20261015-b4-io-uring-fixes-v1-6-c1556f5d7bf5@toxicpanda.com Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- io_uring/io_uring.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -2873,6 +2873,7 @@ struct io_tctx_exit { struct callback_head task_work; struct completion completion; struct io_ring_ctx *ctx; + bool in_cancel; }; static __cold void io_tctx_exit_cb(struct callback_head *cb) @@ -2887,7 +2888,8 @@ static __cold void io_tctx_exit_cb(struc * tctx can be NULL if the queueing of this task_work raced with * work cancelation off the exec path. */ - if (tctx && !atomic_read(&tctx->in_cancel)) + work->in_cancel = tctx && atomic_read(&tctx->in_cancel); + if (tctx && !work->in_cancel) io_uring_del_tctx_node((unsigned long)work->ctx); complete(&work->completion); } @@ -2981,6 +2983,14 @@ static __cold void io_ring_exit_work(str * wait is marked as interruptible. */ wait_for_completion_interruptible(&exit.completion); + /* + * The task removes the node when it is done with its + * cancellation. Give it the time for that: it doesn't get back + * to it as long as it finds new task_work each time it has run + * the old one, and we may be one of many who send it. + */ + if (exit.in_cancel) + schedule_timeout_idle(HZ / 20); mutex_lock(&ctx->uring_lock); } mutex_unlock(&ctx->uring_lock);