From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 798F030C158; Mon, 14 Sep 2026 09:00:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789376436; cv=none; b=dlZxeRgRvtrctjPQGfT4idFdCatl86yJobOPVb9Wk4xzx/OBJVj6SLRa/brVJfcwI9ZZ6bcmnMx9Xqh6fVps6ZKriVC/RJCMEUa68QVWCMKqnMpvHjWSyRh6iwsekRHj5SWIv6GQc1S7u2vpEVbxKKlPMStanbX/p3OO9Drnql8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789376436; c=relaxed/simple; bh=7bt/F0CfVemOLCYjcFdY4goT6DEiXj1lo5PD518miAs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=py756LHAsqviw9qcIaWWcj5jQNVhkPGaw+0zpYVSDOw2EDoYojCog5bbpooVfHTTgV48kOAavCqNCpl1dKmqT/ykU08qwurI9R/bOsW2hZHtLFTpqFMIkAtjYNCHzLBUrhodKTl0pve6b0oz8uCPnqJdhhotA5auyWgZkaTTsrU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=B7GNDCSc; arc=none smtp.client-ip=148.163.158.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="B7GNDCSc" Received: from pps.filterd (m0356516.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 68E61cQU1073456; Mon, 14 Sep 2026 08:59:28 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=pt3fSj eeIvWvADHdEPjDUXMMoaPuoTnloTSzqubqWqg=; b=B7GNDCScsOGqYPNIY9orkN HY8ojE0QQlZ6xyEU8m89/vC8C+tWvny456itzCZHkkHmW1laVd8dkWFsG9raouzO IR1zaJ8DgeqsKKTYNCNWCrZkCwG99La442uSvx8AT1uf6qXM+hcNlklaFEuPDdk/ GqPRirHdQxoajVFyeiI8kJsATQ1ifvpvUmv9uBVVz15mH+kfNEqtpKe/hHHmbVt5 niKh1lSktd1kx+sQXXaWNcMghxKJJs4TZ5GNs+7wdzatSA0e2ROGynKhh3lRU5LK cKWeWJQ8Y9Of2NjArx269SMfbEf6+LROL18rlv7HHKJNDBu3n8SQtcqzU4/t6b6A == Received: from ppma23.wdc07v.mail.ibm.com (5d.69.3da9.ip4.static.sl-reverse.com [169.61.105.93]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4gmv5hgc3b-1 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Mon, 14 Sep 2026 08:59:27 +0000 (GMT) Received: from pps.filterd (ppma23.wdc07v.mail.ibm.com [127.0.0.1]) by ppma23.wdc07v.mail.ibm.com (8.18.1.11/8.18.1.11) with ESMTP id 68E5o6vw1787513; Mon, 14 Sep 2026 08:59:26 GMT Received: from smtprelay03.fra02v.mail.ibm.com ([9.218.2.224]) by ppma23.wdc07v.mail.ibm.com (PPS) with ESMTPS id 4gnjjgmvfy-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 14 Sep 2026 08:59:26 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (smtpav04.fra02v.mail.ibm.com [10.20.54.103]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 68E8xOrP47579618 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 14 Sep 2026 08:59:24 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 734662004B; Mon, 14 Sep 2026 08:59:24 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3944520040; Mon, 14 Sep 2026 08:59:24 +0000 (GMT) Received: from [9.224.77.173] (unknown [9.224.77.173]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 14 Sep 2026 08:59:24 +0000 (GMT) Message-ID: <61b5197f-3a6e-4cbd-8ad7-ca69582309f6@linux.ibm.com> Date: Mon, 14 Sep 2026 10:59:23 +0200 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] nbd: reclassify u->iolock of AF_UNIX sockets To: Josef Bacik Cc: Jens Axboe , Christian Brauner , linux-block@vger.kernel.org, nbd@other.debian.org, linux-kernel@vger.kernel.org, Eric Dumazet , Christian Borntraeger References: <20260713181401.11088-1-borntraeger@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20260713181401.11088-1-borntraeger@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTE0MDEyMSBTYWx0ZWRfX+YlATiqctGpe k1wngUHpBpEIeYRP3aTkIEwCUY4EhsTDKjVSD/bV4HeDw3NX9NXsGGWrevk5sEdMOVcAG4d1We4 jGLh3/TKsPQ7Ms5MnrT8viHwk6MlwpSOdYv123SQz5dUrhNGPbcMKxg+uM/UtB/AiDZX6MxWRHU 3/a4ASoxIkqjldqHV+hzclqKN7tQiJFJo/FTtiscUwJpuNDCO+SXM6K4kxNtZVh4+eYz28WcXXm jHTwe+qJRugknJoHhINdyWAcmfzhNOATR67lsOjGsl2Q2dalndvMt6L7h7sNVH8vnHBNyI1L28S 3h4flERW7YbKUhlD4xYum4jAQfioqaXWZyvIBNoaNEzVvUAWjx++uO+dOUU9bmRX+8HILu19z2n pA86o9cghQKRN9p9oe0jqDbMmghpjH7P671TMRJon/F1Nn1gc9d3qygM+2RZqZH2zIVrTfd5H8H 2lJndpCFadLSlq2fF+w== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTE0MDEyMSBTYWx0ZWRfX0xtS1jCc3bMq 1RkLP/6qJgSPLVkGMilUc9nB1oejdatiOxPZVIbbwgawFMw/BukY8LXLuWQoID+UrFNT6MRWhD/ vkj/pPMMIEDyCPAAtdiR3gls7Yus2Cg= X-Authority-Analysis: v=2.4 cv=Zsx4uN7G c=1 sm=1 tr=0 ts=6aa7b76f cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=LzvJ8H6-aFGr2eQcibkA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: kpOJ9pIp-rtEa6xqL_mdf5hqQ2cMvDos X-Proofpoint-GUID: t3V_b0Wgz2UdNpGKkjelEm7xlBcSKqfu X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-14_02,2026-09-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 impostorscore=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 bulkscore=0 adultscore=0 phishscore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609140121 Am 13.07.26 um 20:14 schrieb Christian Borntraeger: > From: Christian Borntraeger > > in our CI we do get the following when unloading the nbd module. > > [ 120.008698] block nbd0: NBD_DISCONNECT > [ 120.009078] block nbd0: Disconnected due to user request. > [ 120.009413] block nbd0: shutting down sockets > > [ 120.269755] ====================================================== > [ 120.269757] WARNING: possible circular locking dependency detected > [ 120.269759] 7.2.0-rc2-00005-g3e3aa6da87d3 #117 Not tainted > [ 120.269761] ------------------------------------------------------ > [ 120.269762] modprobe/8168 is trying to acquire lock: > [ 120.269764] 000001e67da57138 (set->srcu){.+.?}-{0:0}, at: __synchronize_srcu+0x36/0x210 > [ 120.269775] > but task is already holding lock: > [ 120.269776] 000001bf63462d90 (&q->elevator_lock){+.+.}-{3:3}, at: elevator_change+0xac/0x1d0 > [ 120.269784] which lock already depends on the new lock. > > [ 120.269786] the existing dependency chain (in reverse order) is: > [ 120.269788] > -> #5 (&q->elevator_lock){+.+.}-{3:3}: > [ 120.269792] lock_acquire+0x150/0x3f0 > [ 120.269795] __mutex_lock+0xba/0xdc0 > [ 120.269799] mutex_lock_nested+0x32/0x40 > [ 120.269802] elevator_change+0xac/0x1d0 > [ 120.269804] elv_iosched_store+0x194/0x1e0 > [ 120.269807] kernfs_fop_write_iter+0x18c/0x270 > [ 120.269810] vfs_write+0x23c/0x380 > [ 120.269813] ksys_write+0x88/0x120 > [ 120.269816] __do_syscall+0x170/0x750 > [ 120.269818] system_call+0x72/0x90 > [ 120.269821] > -> #4 (&q->q_usage_counter(io)#18){++++}-{0:0}: > [ 120.269871] lock_acquire+0x150/0x3f0 > [ 120.269873] blk_alloc_queue+0x2fe/0x340 > [ 120.269876] blk_mq_alloc_queue+0x6c/0xe0 > [ 120.269879] __blk_mq_alloc_disk+0x2a/0x80 > [ 120.269881] dasd_gendisk_alloc+0xd4/0x200 > [ 120.269885] dasd_state_known_to_basic+0x34/0x1f0 > [ 120.269890] dasd_change_state+0x28a/0x570 > [ 120.269892] dasd_set_target_state+0x76/0xf0 > [ 120.269895] dasd_generic_set_online+0xc8/0x2c0 > [ 120.269897] ccw_device_set_online+0xc6/0x550 > [ 120.269901] online_store+0xd2/0x270 > [ 120.269904] kernfs_fop_write_iter+0x18c/0x270 > [ 120.269906] vfs_write+0x23c/0x380 > [ 120.269909] ksys_write+0x88/0x120 > [ 120.269912] __do_syscall+0x170/0x750 > [ 120.269914] system_call+0x72/0x90 > [ 120.269916] > -> #3 (fs_reclaim){+.+.}-{0:0}: > [ 120.269920] lock_acquire+0x150/0x3f0 > [ 120.269922] __fs_reclaim_acquire+0x44/0x50 > [ 120.269925] fs_reclaim_acquire+0xbe/0x100 > [ 120.269927] kmem_cache_alloc_noprof+0x6c/0x6d0 > [ 120.269931] alloc_empty_file+0x58/0x150 > [ 120.269933] dentry_open+0x3c/0xa0 > [ 120.269935] pidfs_alloc_file+0xba/0x130 > [ 120.269940] pidfd_prepare+0x8c/0xf0 > [ 120.269945] scm_recv_unix+0xb0/0x130 > [ 120.269949] __unix_dgram_recvmsg+0x2aa/0x430 > [ 120.269954] sock_recvmsg+0x70/0xd0 > [ 120.269956] ____sys_recvmsg+0x8a/0x190 > [ 120.269958] ___sys_recvmsg+0x88/0xd0 > [ 120.269960] __sys_recvmsg+0x76/0xd0 > [ 120.269962] __do_sys_socketcall+0x40a/0x460 > [ 120.269964] __do_syscall+0x170/0x750 > [ 120.269967] system_call+0x72/0x90 > [ 120.269969] > -> #2 (&u->iolock){+.+.}-{3:3}: > [ 120.269973] lock_acquire+0x150/0x3f0 > [ 120.269975] __mutex_lock+0xba/0xdc0 > [ 120.269978] mutex_lock_nested+0x32/0x40 > [ 120.269981] unix_stream_read_generic+0x11e/0xa60 > [ 120.269985] unix_stream_recvmsg+0xae/0xc0 > [ 120.269988] sock_recvmsg+0x70/0xd0 > [ 120.269990] __sock_xmit+0xf0/0x1b0 [nbd] > [ 120.269997] nbd_handle_reply+0x284/0x770 [nbd] > [ 120.270001] recv_work+0x10c/0x290 [nbd] > [ 120.270004] process_one_work+0x2ba/0x800 > [ 120.270009] worker_thread+0x21a/0x400 > [ 120.270012] kthread+0x164/0x190 > [ 120.270016] __ret_from_fork+0x4c/0x340 > [ 120.270020] ret_from_fork+0xa/0x30 > [ 120.270022] > -> #1 (&cmd->lock){+.+.}-{3:3}: > [ 120.270026] lock_acquire+0x150/0x3f0 > [ 120.270028] __mutex_lock+0xba/0xdc0 > [ 120.270031] mutex_lock_nested+0x32/0x40 > [ 120.270034] nbd_queue_rq+0x38/0x70 [nbd] > [ 120.270037] blk_mq_dispatch_rq_list+0x19c/0x540 > [ 120.270040] __blk_mq_do_dispatch_sched+0x3ce/0x3e0 > [ 120.270043] __blk_mq_sched_dispatch_requests+0x198/0x1e0 > [ 120.270046] blk_mq_sched_dispatch_requests+0x3c/0x90 > [ 120.270049] blk_mq_run_work_fn+0x9e/0x180 > [ 120.270052] process_one_work+0x2ba/0x800 > [ 120.270055] worker_thread+0x21a/0x400 > [ 120.270058] kthread+0x164/0x190 > [ 120.270060] __ret_from_fork+0x4c/0x340 > [ 120.270063] ret_from_fork+0xa/0x30 > [ 120.270065] > -> #0 (set->srcu){.+.?}-{0:0}: > [ 120.270069] check_prev_add+0x160/0xf40 > [ 120.270073] __lock_acquire+0x12aa/0x15a0 > [ 120.270075] lock_sync+0xf4/0x190 > [ 120.270077] __synchronize_srcu+0x5c/0x210 > [ 120.270080] elevator_switch+0x190/0x340 > [ 120.270082] elevator_change+0x152/0x1d0 > [ 120.270084] elevator_set_none+0x44/0x90 > [ 120.270087] blk_unregister_queue+0xd4/0x130 > [ 120.270090] __del_gendisk+0x172/0x3c0 > [ 120.270093] del_gendisk+0x86/0xb0 > [ 120.270096] nbd_dev_remove+0x30/0x90 [nbd] > [ 120.270100] nbd_cleanup+0x11a/0x3a8 [nbd] > [ 120.270104] __do_sys_delete_module+0x18e/0x340 > [ 120.270107] __do_syscall+0x170/0x750 > [ 120.270110] system_call+0x72/0x90 > [ 120.270112] > other info that might help us debug this: > > [ 120.270114] Chain exists of: > set->srcu --> &q->q_usage_counter(io)#18 --> &q->elevator_lock > > [ 120.270120] Possible unsafe locking scenario: > > [ 120.270121] CPU0 CPU1 > [ 120.270122] ---- ---- > [ 120.270124] lock(&q->elevator_lock); > [ 120.270126] lock(&q->q_usage_counter(io)#18); > [ 120.270129] lock(&q->elevator_lock); > [ 120.270132] sync(set->srcu); > [ 120.270134] > *** DEADLOCK *** > > [ 120.270136] 2 locks held by modprobe/8168: > [ 120.270138] #0: 000001bf44ce11e0 (&set->update_nr_hwq_lock){++++}-{3:3}, at: del_gendisk+0x76/0xb0 > [ 120.270145] #1: 000001bf63462d90 (&q->elevator_lock){+.+.}-{3:3}, at: elevator_change+0xac/0x1d0 > [ 120.270152] > stack backtrace: > [ 120.270155] CPU: 48 UID: 0 PID: 8168 Comm: modprobe Not tainted 7.2.0-rc2-00005-g3e3aa6da87d3 #117 PREEMPT > [ 120.270157] Hardware name: IBM 9175 ME1 701 (LPAR) > [ 120.270158] Call Trace: > [ 120.270158] [<000002c7d1164dde>] dump_stack_lvl+0xae/0x108 > [ 120.270160] [<000002c7d126e5b4>] print_circular_bug+0x1a4/0x230 > [ 120.270163] [<000002c7d126e7cc>] check_noncircular+0x18c/0x1b0 > [ 120.270165] [<000002c7d126fb80>] check_prev_add+0x160/0xf40 > [ 120.270167] [<000002c7d12736fa>] __lock_acquire+0x12aa/0x15a0 > [ 120.270168] [<000002c7d1275ce4>] lock_sync+0xf4/0x190 > [ 120.270169] [<000002c7d129c8fc>] __synchronize_srcu+0x5c/0x210 > [ 120.270171] [<000002c7d1bb4790>] elevator_switch+0x190/0x340 > [ 120.270173] [<000002c7d1bb4a92>] elevator_change+0x152/0x1d0 > [ 120.270174] [<000002c7d1bb53c4>] elevator_set_none+0x44/0x90 > [ 120.270176] [<000002c7d1bbee84>] blk_unregister_queue+0xd4/0x130 > [ 120.270177] [<000002c7d1bdff42>] __del_gendisk+0x172/0x3c0 > [ 120.270179] [<000002c7d1be0216>] del_gendisk+0x86/0xb0 > [ 120.270182] [<000002c751b2adc0>] nbd_dev_remove+0x30/0x90 [nbd] > [ 120.270185] [<000002c751b30d72>] nbd_cleanup+0x11a/0x3a8 [nbd] > [ 120.270189] [<000002c7d12c72ce>] __do_sys_delete_module+0x18e/0x340 > [ 120.270191] [<000002c7d22dc170>] __do_syscall+0x170/0x750 > [ 120.270192] [<000002c7d22f0db2>] system_call+0x72/0x90 > [ 120.270194] INFO: lockdep is turned off. > > this seems to be a false positive. > > Commit d532cddb6c60 ("nbd: Reclassify sockets to avoid lockdep > circular dependency") already reclassifies sk_lock and slock of > sockets handed to nbd, including AF_UNIX ones, precisely to keep > lockdep from reporting. > That is not sufficient for AF_UNIX: the unix stream/dgram recvmsg and > sendmsg paths do not serialize on sk_lock but on unix_sk(sk)->iolock, > and that mutex keeps the generic "&u->iolock" class shared by every > AF_UNIX socket in the system. > > Teach lockdep about the lock instances to avoid this report. > This gets rid of the lockdep warning. > > Assisted-by: Claude:claude-fable-5 > Signed-off-by: Christian Borntraeger Ping. > --- > drivers/block/nbd.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c > index 8f10762e90ef..a811e431b47a 100644 > --- a/drivers/block/nbd.c > +++ b/drivers/block/nbd.c > @@ -32,6 +32,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -1241,6 +1242,7 @@ static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd, > #ifdef CONFIG_DEBUG_LOCK_ALLOC > static struct lock_class_key nbd_key[3]; > static struct lock_class_key nbd_slock_key[3]; > +static struct lock_class_key nbd_unix_iolock_key; > > static void nbd_reclassify_socket(struct socket *sock) > { > @@ -1267,6 +1269,17 @@ static void nbd_reclassify_socket(struct socket *sock) > &nbd_slock_key[2], > "sk_lock-AF_UNIX-NBD", > &nbd_key[2]); > + /* > + * The AF_UNIX stream recvmsg/sendmsg paths serialize on > + * u->iolock, not sk_lock, so it must be reclassified as > + * well. A held mutex cannot be reclassified; skip it in > + * that case, as sock_allow_reclassification() does for > + * sk_lock. > + */ > + if (!mutex_is_locked(&unix_sk(sk)->iolock)) > + lockdep_set_class_and_name(&unix_sk(sk)->iolock, > + &nbd_unix_iolock_key, > + "&u->iolock-NBD"); > break; > } > }