From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-0031df01.pphosted.com (mx0a-0031df01.pphosted.com [205.220.168.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3BF2037CD41 for ; Fri, 15 May 2026 06:18:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=205.220.168.131 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778825928; cv=none; b=QiqLwr4krQ/4c+oGWkpCnFR6TBpH2eFnfRZUrwBodHwd9aVrm6dpvUAyFcs68mY+NSz0ORdEovtSmEP2Vrieg8mdOa42dtHsJ12yPRZ7D0W0iy0robM0dOseVfV6EzUUS8WKGU+LOrpgLaS9b9e51v03b+j+QynXWlPya3BEdfw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778825928; c=relaxed/simple; bh=Y6e/eCfvQGBEEkdB9zIuugcIE4hbVc77QyCSGQIK8k0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=CpIwtTRH2BllWKXG4gkI3B8GSZUQlUWaI6k4nMT+B2Mv8NpDcBTQXQ0gL8TZs5yymvv8TOFdtgC75JWe9KMZenpS5RSl6OIwCd/9UD4L71QzblYbHaIxzDfGYVmsTo1cYf9ypIz1x0X4U6gTeEKcHiPDR8+x+YlRSpblp1NLpEM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oss.qualcomm.com; spf=pass smtp.mailfrom=oss.qualcomm.com; dkim=pass (2048-bit key) header.d=qualcomm.com header.i=@qualcomm.com header.b=Fq3ISk47; dkim=pass (2048-bit key) header.d=oss.qualcomm.com header.i=@oss.qualcomm.com header.b=DIwGu2Pi; arc=none smtp.client-ip=205.220.168.131 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oss.qualcomm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oss.qualcomm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=qualcomm.com header.i=@qualcomm.com header.b="Fq3ISk47"; dkim=pass (2048-bit key) header.d=oss.qualcomm.com header.i=@oss.qualcomm.com header.b="DIwGu2Pi" Received: from pps.filterd (m0279864.ppops.net [127.0.0.1]) by mx0a-0031df01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 64F5KUjD4022631 for ; Fri, 15 May 2026 06:18:46 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qualcomm.com; h= cc:content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=qcppdkim1; bh= TXJH+kCot1mDQ/XXpZpurKH5KBj+DptFtIRpapZ8BN0=; b=Fq3ISk47skZQpqAU BJ7vLdInZuI2jcvmsKlica7bYhn9HtE8EsP9H9ktrCqYiCakd2zeozzXnQHbuwme Wno8f4XH8A+dh7U5/zAWkrxiY4xLCqX2epwfe0KUEk1TpiR4IwqdyDeCHjURKkkr c1HXC2MGNpeHqAH9hNKDdn+thTccRQeaBazn5gCwMNsH1Uwnu02MzpyVaxFzTvgW cKOVHiqdwvf8mFHGlrPNNE8JGYppzzzs9dnYFAG8NmBFKWTd/l4NzWmaKTPqRmtm E++0B+b6wva8rcKmnJ7SJtOgEGZcAhaziww7IPfc8rZHLnfP0sqsAT5CvMEEVCZ3 CZexbw== Received: from mail-pl1-f197.google.com (mail-pl1-f197.google.com [209.85.214.197]) by mx0a-0031df01.pphosted.com (PPS) with ESMTPS id 4e5m1rsujd-1 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NOT) for ; Fri, 15 May 2026 06:18:46 +0000 (GMT) Received: by mail-pl1-f197.google.com with SMTP id d9443c01a7336-2baedd2fd43so55913855ad.1 for ; Thu, 14 May 2026 23:18:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oss.qualcomm.com; s=google; t=1778825925; x=1779430725; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :from:to:cc:subject:date:message-id:reply-to; bh=TXJH+kCot1mDQ/XXpZpurKH5KBj+DptFtIRpapZ8BN0=; b=DIwGu2Pic4U0OaC4EepPej276hyj0+8xLzC7GM0lpoVttCijiYZ2L4PO9kj6eC5VI4 V49u7IK99Knxx8pyRCcDjdyRyGgICcqq7l++WtRsnjWg9mmY2ZfIIhfb5ZdlmXcXnYAR lH8W6eAh9uAnu2hmmoymWE3+bZRgggRzo3EUSZbk0jFdd82nHnLi0bkNb+OCjT/fO4PZ /ZeRL88j8OGPY49aRcK7Kue/eRHDghTcPwwdnZalkGtKuZriuK4vAupYxZKVZwM9aimr 7Lec6ZS6loBxv1/O8mo1btE/WtSZxHY6WxCOwhP7AwgjZfes0+L1yxWSsNKO3HwdFsQ8 606w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778825925; x=1779430725; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=TXJH+kCot1mDQ/XXpZpurKH5KBj+DptFtIRpapZ8BN0=; b=PQTV6Zwg7E7dY0zExcPLfupfKcIKFV/516PWVsVT50+oFGmt0rBj4KG1bxq036p3HT VEPKtLM3XIHpCXECrL2EVLCVqoexSKHxoNPeyqypFWiCZVmvw74TVcOMQTbArnKVBt3U eMwmdMvyx99sLj0hrmMPpM6riZrUH6z7y/U0qAl4onjokSYcK7gBq84uvOzDh0m8d+Jh LdV+r5azliPc7fymifUPv+qm8Zr44hwX3JopyHHCQkPl+fggEGoAovwsyLYXTFuE8lj/ lEnWBKdFMpQ6ltApXXmgfjyrWfxYFBLqABX5P5wo8gfNohb/K9WgWt4bh/qJ4TzPo/BG widQ== X-Forwarded-Encrypted: i=1; AFNElJ8uSMmRd6j6sbe9BTYboF8j00G65U6PoYhFO09MlwXhXZKVjNl90K3l3FSzdnIESoo9GyELOws405lZU4I=@vger.kernel.org X-Gm-Message-State: AOJu0Yx95C83Er9Zk2xPuU4E7OoO1hGB/+uESOHleT73yq1kb5x9JAPz 3ausVkWcwR+2eE1RyrR/qkNoKJC0a02eRoYmPVatUi/oMyEfDXxzz2G7OZJBt04iBlng9d5CrDv gpRGXGBM0gdFb39FcdpLNzo6DcMer2nCYSczkULEnoR8l9bYO3LtTebs1vTX3kASH+Tk= X-Gm-Gg: Acq92OGeWHvbzhaRAJOkXoSgBZwMlzZYO9w2oJbaSV2V8Gxtlkv02KNo8KUlaEJnmQd 28LJLyMYL4+VVy+9D64XAs5/jihyEKG/1En+nAKbK9oS6ufmjWYieeb3KM63/ZyIn0l008tLjWc WHaThKUiIw6+CQOAPRppDMQedgH7kk36uEsOngzhnGeskg5ezpkP3pGRf7kabzZN91rFBuprR6n xDVavLZJBxHNPeKoRuWIJCAt50IKMnxSf3xRKIbguBldMohsamdNZxOHpFiJofsYqMKBzU0zCDc WGHLhzYGpQd7/YYy3uyfGyvVbTTCRidhJCmY+KNnwuJsx511DS5ymaUI6ueqFlG2F1p8lusGv50 KZmLB2JTsp9DV0xtKI8XlCFTNsLd4qt5ozuJdfL4b+sPD6gLFriOMCABmUAAH6lYrLPC60gHtSQ E04HLhRzfq2/SkOR0= X-Received: by 2002:a17:903:3c4c:b0:2bd:83e1:5613 with SMTP id d9443c01a7336-2bd83e157a2mr23657755ad.20.1778825925324; Thu, 14 May 2026 23:18:45 -0700 (PDT) X-Received: by 2002:a17:903:3c4c:b0:2bd:83e1:5613 with SMTP id d9443c01a7336-2bd83e157a2mr23657415ad.20.1778825924781; Thu, 14 May 2026 23:18:44 -0700 (PDT) Received: from [10.249.31.163] (tpe-colo-wan-fw-bordernet.qualcomm.com. [103.229.16.4]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2bd5c0600b4sm48730865ad.28.2026.05.14.23.18.41 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 May 2026 23:18:44 -0700 (PDT) Message-ID: <6611f3ea-b70f-45c7-9332-235647643a49@oss.qualcomm.com> Date: Fri, 15 May 2026 14:18:40 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched: flush plug in schedule_preempt_disabled() to prevent deadlock To: Ming Lei , Peter Zijlstra Cc: Tejun Heo , Jens Axboe , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar , Juri Lelli , Vincent Guittot , Michael Wu , Thomas Gleixner References: <20260512085939.1107372-1-tom.leiming@gmail.com> <20260512120431.GC1889694@noisy.programming.kicks-ass.net> <20260512124021.GA2214256@noisy.programming.kicks-ass.net> <20260513073039.GG1889694@noisy.programming.kicks-ass.net> Content-Language: en-US From: Xiaosen In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: -NQ98DqiXz65lln8ymwPNX_WxEd6g80F X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTE1MDA2MCBTYWx0ZWRfXzmYvdhLLYuJ0 tlhQprGUm4fzpzPLMP+5dbblQVzQGpZvj8S+ROe3T7GlV6xKvrZNCdolY9zef/l6T0h8ntCDBhP tOqCT00xE1Oc9sxOmgudgniVJ8CiaC69kvtQzeEmXJ/L5+fdCDMQkS5umiCjT303N0WPZ3NUYMO 80T2H1ToTQUFKnvx8ZMEz2osWJ4zNN2tHvS+gWH2OBj2diQAFlxmpMuY6shz5ia3hmQ7EFfg75n zdS7obtXeqSg38WyGwQt3vL0ou8fxD0dnd5GmIFdKuIO5w7b/CNjUVr0icmb//E+PthiP97ykEz 11HwVkPB6BpKSWUgNyOdybJLaUf5hqjlP9Pxs6M4Dceumx6lkJUJ9O8A5QBqVt2jRbK4SYAdqn+ qj8MRl4d6Ume16zHcOQ2gtktK8Y7UftLsAkb0BOAaEVZBcdpRqBCI2nJkxJSRy26efrbC5ukqTZ KCJQbx9qrbI9+AYkfWw== X-Proofpoint-ORIG-GUID: -NQ98DqiXz65lln8ymwPNX_WxEd6g80F X-Authority-Analysis: v=2.4 cv=JPELdcKb c=1 sm=1 tr=0 ts=6a06bac6 cx=c_pps a=cmESyDAEBpBGqyK7t0alAg==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=DJpcGTmdVt4CTyJn9g5Z:22 a=VwQbUJbxAAAA:8 a=1XWaLZrsAAAA:8 a=6Ujbnq6iAAAA:8 a=EUspDBNiAAAA:8 a=srUJ046Ut8OOLMdfYg8A:9 a=QEXdDO2ut3YA:10 a=1OuFwYUASf3TG4hYMiVC:22 a=-sNzveBoo8RYOSiOai2t:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-15_01,2026-05-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 clxscore=1015 phishscore=0 priorityscore=1501 spamscore=0 malwarescore=0 suspectscore=0 impostorscore=0 adultscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605150060 https://lore.kernel.org/lkml/20260427183848.698551-2-jstultz@google.com/ The above change can resolve the deadlock I reported before by setting task's state to TASK_RUNNING before switching context. There is the likely alternative fix below. https://lore.kernel.org/lkml/20260512025635.2840817-1-jstultz@google.com/ Regards, Xiaosen On 5/13/2026 4:08 PM, Ming Lei wrote: > On Wed, May 13, 2026 at 09:30:39AM +0200, Peter Zijlstra wrote: >> On Wed, May 13, 2026 at 10:07:03AM +0800, Ming Lei wrote: >>> On Tue, May 12, 2026 at 07:16:36AM -1000, Tejun Heo wrote: >>>> Hello, Ming. >>>> >>>> On Tue, May 12, 2026 at 11:45:14PM +0800, Ming Lei wrote: >>>>> On Tue, May 12, 2026 at 02:40:21PM +0200, Peter Zijlstra wrote: >>>>>> On Tue, May 12, 2026 at 02:04:32PM +0200, Peter Zijlstra wrote: >>>>>>> On Tue, May 12, 2026 at 04:59:39PM +0800, Ming Lei wrote: >>>>>>>> On preemptible kernels, a deadlock can occur when a task with plugged IO >>>>>>>> calls schedule_preempt_disabled(): >>>>>>>> >>>>>>>> schedule_preempt_disabled() >>>>>>>> sched_preempt_enable_no_resched() // preemption now enabled >>>>>>>> schedule() // <-- preemption can happen here >>>>>>>> sched_submit_work() >>>>>>>> blk_flush_plug() >>>>>>>> >>>>>>>> After sched_preempt_enable_no_resched() re-enables preemption, the task >>>>>>>> can be preempted (e.g., by a higher-priority RT task) before reaching >>>>>>>> blk_flush_plug() in sched_submit_work(). Since the task's state is >>>>>>>> already TASK_UNINTERRUPTIBLE (set by the mutex/rwsem slowpath caller), >>>>>>>> requests in current->plug remain unflushed for an unbounded time. >>>>>>>> >>>>>>>> If another task depends on those plugged requests to make progress (e.g., >>>>>>>> to release a lock the sleeping task needs), a deadlock results: >>>>>>>> >>>>>>>> - Task A (writeback worker): holds plugged IO, preempted before >>>>>>>> flushing, stuck on run queue behind higher-priority work >>>>>>>> - Task B: waiting for IO completion from Task A's plug, holds a lock >>>>>>>> that Task A needs to be woken up >>>> >>>> My memory is hazy around io_schedule but the above reads really weird to me. >>>> A task, regardless of its current state stays on the runqueue when >>>> preempted, so the condition is temporary. As soon as the preempted task can >>>> get CPU, it should unwind the situation. That's not a deadlock. Is the >>>> problem that there can be preemption-induced delay in flushing the plugs? >>> >>> IMO, preempting a `!TASK_RUNNING` task can be thought as effective sleep, >> >> No it cannot be. Preemption ignores task state. > > Yeah, I get similar conclusion too with AI's assistance. > > But both two reports show that the preempted task aren't switched back for > long enough time, can you share any idea for Michael & Xiaosen to investigate > further from scheduler side? > > https://lore.kernel.org/linux-block/20260417082744.30124-1-michael@allwinnertech.com/ > > https://lore.kernel.org/linux-block/5660795d-87de-46f5-add4-7729a02225ef@oss.qualcomm.com/ > > > Thanks, > Ming