From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (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 8F3DE17A2FA; Mon, 4 Aug 2025 07:51:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754293916; cv=none; b=kuOXvOtBlOVI2RbnSIhstWzoHL3V8+PnbrqXrPQu2WsI/zzYy7jRl4/0X7jU7niGQgM0be+GwvbsRRtfmWYuyUgdE5YhPo4H3Fq8W6DBUrcUno5imNyAMPkvkzvMdCM0euLtdyH7yd+E77X8rDOa4UyG1mmYiIxLrPasdBM8etQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754293916; c=relaxed/simple; bh=LrG+/tvtivwg0ZcBSe2od2nC/VpaBwV8LhuTSc+IHkI=; h=Subject:To:Cc:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=C1eSMMr/0ItUmtuabku6ubeZ4jjHbDi0Eb2Dd6qBEPeSchE1p0Ni/F/uGAWeYqrH/vcmxsxeWJafgcl+Uw8qfyRlLDyw5aXp9JCgVVkgJRSSXAApnWXBaDGWsvlisg0i7oftJnLr70nhedMqaHhHJp3JeUplGiRxeCzGL8JbT+c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4bwTKM3Ts2zKHMSj; Mon, 4 Aug 2025 15:51:51 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 7C10A1A0359; Mon, 4 Aug 2025 15:51:50 +0800 (CST) Received: from [10.174.179.143] (unknown [10.174.179.143]) by APP4 (Coremail) with SMTP id gCh0CgBXIBGUZpBoQBoXCg--.28613S3; Mon, 04 Aug 2025 15:51:50 +0800 (CST) Subject: Re: [PATCH] block: prevent deadlock in del_gendisk() To: Ujwal Kundur , axboe@kernel.dk Cc: ming.lei@redhat.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+2e9e529ac0b319316453@syzkaller.appspotmail.com, "yukuai (C)" References: <20250803134114.2707-1-ujwal.kundur@gmail.com> From: Yu Kuai Message-ID: Date: Mon, 4 Aug 2025 15:51:48 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20250803134114.2707-1-ujwal.kundur@gmail.com> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:gCh0CgBXIBGUZpBoQBoXCg--.28613S3 X-Coremail-Antispam: 1UD129KBjvJXoW7tF13CrWDAFyUZryDWFy5XFb_yoW8KFyDpF ZxWFs0k340vr1v93WUta47GF18Gw1DWFyIkryxJFy2vrnFyr9rtr18KFyxurW0yrZ7urs2 qa1qqFsxur48AFDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvjb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUGVWUXwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JMxk0xIA0c2IEe2xFo4CEbIxvr21lc7CjxVAaw2AF wI0_JF0_Jw1l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4 xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r126r1D MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I 0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY6I8E87Iv67AKxVWU JVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvjxUot CzDUUUU X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ Hi, ÔÚ 2025/08/03 21:41, Ujwal Kundur дµÀ: > A potential unsafe locking scenario presents itself when > mutex_lock(&disk->open_mutex) is called with reader's lock held on > update_nr_hwq_lock: > CPU0 CPU1 > ---- ---- > rlock(&set->update_nr_hwq_lock) > lock(&nbd->config_lock); > lock(&set->update_nr_hwq_lock); > lock(&disk->open_mutex) > This problem is already fixed inside nbd by: 8b428f42f3ed ("nbd: fix lockdep deadlock warning") Thanks, Kuai > When the gendisk is added back concurrently, a writer's lock is > attempted to be held on update_nr_hwq_lock while holding other locks in > the call-path, becoming a potential source of deadlock(s). > > Scope read-critical section to blk_unregister_queue, which is the only > function that interacts with switching elevator and requires > synchronization with update_nr_hwq_lock. > > Reported-by: syzbot+2e9e529ac0b319316453@syzkaller.appspotmail.com > Signed-off-by: Ujwal Kundur > --- > block/genhd.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > mode change 100644 => 100755 block/genhd.c > > diff --git a/block/genhd.c b/block/genhd.c > old mode 100644 > new mode 100755 > index c26733f6324b..b56f09f5699b > --- a/block/genhd.c > +++ b/block/genhd.c > @@ -696,6 +696,7 @@ static void __del_gendisk(struct gendisk *disk) > struct block_device *part; > unsigned long idx; > bool start_drain; > + struct blk_mq_tag_set *set = q->tag_set; > > might_sleep(); > > @@ -740,7 +741,9 @@ static void __del_gendisk(struct gendisk *disk) > bdi_unregister(disk->bdi); > } > > + down_read(&set->update_nr_hwq_lock); > blk_unregister_queue(disk); > + up_read(&set->update_nr_hwq_lock); > > kobject_put(disk->part0->bd_holder_dir); > kobject_put(disk->slave_dir); > @@ -808,20 +811,15 @@ static void disable_elv_switch(struct request_queue *q) > */ > void del_gendisk(struct gendisk *disk) > { > - struct blk_mq_tag_set *set; > unsigned int memflags; > > if (!queue_is_mq(disk->queue)) { > __del_gendisk(disk); > } else { > - set = disk->queue->tag_set; > - > disable_elv_switch(disk->queue); > > memflags = memalloc_noio_save(); > - down_read(&set->update_nr_hwq_lock); > __del_gendisk(disk); > - up_read(&set->update_nr_hwq_lock); > memalloc_noio_restore(memflags); > } > } >