From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id DFF64EEEC00 for ; Fri, 15 Sep 2023 19:20:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1694805624; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=Zb0E9AFZNO1Wrp1PzpySOgOOIbk+4PwwFCZ8VPTZS9g=; b=aR7COZuTb+7vw0v+mUC2Zo8exMPIk+EOj7pXH6AAUd0/kJS9THif5QWdsUBCkhbP1AiK+3 YwpMZJ9fMI6+OOTqmg+4Dee2wSrKwGoEf/wAW5Q0FBthy+ydQ1+Bwk4zQ/soIFl67wDAT9 NGVDCS09dz+WH9EJTJfHxs0eZvjlprc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-70-eRs5jCMqMaySiL0C8muAVQ-1; Fri, 15 Sep 2023 15:20:21 -0400 X-MC-Unique: eRs5jCMqMaySiL0C8muAVQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2A5CC1818E53; Fri, 15 Sep 2023 19:20:19 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com [10.30.29.100]) by smtp.corp.redhat.com (Postfix) with ESMTP id 16F7A409746E; Fri, 15 Sep 2023 19:20:19 +0000 (UTC) Received: from mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (localhost [IPv6:::1]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id D53F4194658C; Fri, 15 Sep 2023 19:20:13 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) by mm-prod-listman-01.mail-001.prod.us-east-1.aws.redhat.com (Postfix) with ESMTP id 574471946588 for ; Fri, 15 Sep 2023 19:13:29 +0000 (UTC) Received: by smtp.corp.redhat.com (Postfix) id 384C81CBC3; Fri, 15 Sep 2023 19:13:24 +0000 (UTC) Received: from file1-rdu.file-001.prod.rdu2.dc.redhat.com (unknown [10.11.5.21]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 22EF928FD; Fri, 15 Sep 2023 19:13:23 +0000 (UTC) Received: by file1-rdu.file-001.prod.rdu2.dc.redhat.com (Postfix, from userid 12668) id CE95130C2C07; Fri, 15 Sep 2023 19:13:23 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by file1-rdu.file-001.prod.rdu2.dc.redhat.com (Postfix) with ESMTP id C98D03FB7D; Fri, 15 Sep 2023 21:13:23 +0200 (CEST) Date: Fri, 15 Sep 2023 21:13:23 +0200 (CEST) From: Mikulas Patocka To: Mike Snitzer In-Reply-To: Message-ID: References: <4f5737f0-9299-4968-8cb5-07c7645bbffd@kernel.dk> <514767b4-5b2a-4f8e-a6ba-6722ddac5330@kernel.dk> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Subject: Re: [dm-devel] DM brokeness with NOWAIT X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , "dm-devel@redhat.com" Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, 15 Sep 2023, Mike Snitzer wrote: > On Fri, Sep 15 2023 at 12:14P -0400, > Jens Axboe wrote: > > > On 9/15/23 10:04 AM, Jens Axboe wrote: > > > Hi, > > > > > > Threw some db traffic into my testing mix, and that ended in tears > > > very quickly: > > > > > > CPU: 7 PID: 49609 Comm: ringbuf-read.t Tainted: G W 6.6.0-rc1-g39956d2dcd81 #129 > > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 > > > Call Trace: > > > > > > dump_stack_lvl+0x11d/0x1b0 > > > __might_resched+0x3c3/0x5e0 > > > ? preempt_count_sub+0x150/0x150 > > > mempool_alloc+0x1e2/0x390 > > > ? sanity_check_pinned_pages+0x23/0x1010 > > > ? mempool_resize+0x7d0/0x7d0 > > > bio_alloc_bioset+0x417/0x8c0 > > > ? bvec_alloc+0x200/0x200 > > > ? __gup_device_huge+0x900/0x900 > > > bio_alloc_clone+0x53/0x100 > > > dm_submit_bio+0x27f/0x1a20 > > > ? lock_release+0x4b7/0x670 > > > ? pin_user_pages_fast+0xb6/0xf0 > > > ? blk_try_enter_queue+0x1a0/0x4d0 > > > ? dm_dax_direct_access+0x260/0x260 > > > ? rcu_is_watching+0x12/0xb0 > > > ? blk_try_enter_queue+0x1cc/0x4d0 > > > __submit_bio+0x239/0x310 > > > ? __bio_queue_enter+0x700/0x700 > > > ? kvm_clock_get_cycles+0x40/0x60 > > > ? ktime_get+0x285/0x470 > > > submit_bio_noacct_nocheck+0x4d9/0xb80 > > > ? should_fail_request+0x80/0x80 > > > ? preempt_count_sub+0x150/0x150 > > > ? folio_flags+0x6c/0x1e0 > > > submit_bio_noacct+0x53e/0x1b30 > > > blkdev_direct_IO.part.0+0x833/0x1810 > > > ? rcu_is_watching+0x12/0xb0 > > > ? lock_release+0x4b7/0x670 > > > ? blkdev_read_iter+0x40d/0x530 > > > ? reacquire_held_locks+0x4e0/0x4e0 > > > ? __blkdev_direct_IO_simple+0x780/0x780 > > > ? rcu_is_watching+0x12/0xb0 > > > ? __mark_inode_dirty+0x297/0xd50 > > > ? preempt_count_add+0x72/0x140 > > > blkdev_read_iter+0x2a4/0x530 > > > ? blkdev_write_iter+0xc40/0xc40 > > > io_read+0x369/0x1490 > > > ? rcu_is_watching+0x12/0xb0 > > > ? io_writev_prep_async+0x260/0x260 > > > ? __fget_files+0x279/0x410 > > > ? rcu_is_watching+0x12/0xb0 > > > io_issue_sqe+0x18a/0xd90 > > > io_submit_sqes+0x970/0x1ed0 > > > __do_sys_io_uring_enter+0x14d4/0x2650 > > > ? io_submit_sqes+0x1ed0/0x1ed0 > > > ? rcu_is_watching+0x12/0xb0 > > > ? __do_sys_io_uring_register+0x3f6/0x2190 > > > ? io_req_caches_free+0x500/0x500 > > > ? ksys_mmap_pgoff+0x85/0x5b0 > > > ? rcu_is_watching+0x12/0xb0 > > > ? trace_irq_enable.constprop.0+0xd0/0x100 > > > do_syscall_64+0x39/0xb0 > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > which seems to demonstrate a misunderstanding on what REQ_NOWAIT is > > > about. In particulary, it seems to assume you can then submit with > > > atomic context? DM does an rcu_read_lock() and happily proceeds to > > > attempt to submit IO under RCU being disabled. > > > > Did a quick check to see where this came from, and it got added with: > > > > commit 563a225c9fd207326c2a2af9d59b4097cb31ce70 > > Author: Mike Snitzer > > Date: Sat Mar 26 21:08:36 2022 -0400 > > > > dm: introduce dm_{get,put}_live_table_bio called from dm_submit_bio > > > > which conspiciously doesn't include any numbers on why this is necessary > > or a good thing, and notably probably wasn't tested? This landed in 5.19 > > fwiw. > > Don't recall what I was thinking, and I clearly didn't properly test > either... should've consulted Mikulas. Sorry for the trouble. > > Would you like to send a formal patch with your Signed-off-by and I'll > mark it for stable@ and get it to Linus? > > Mike We could revert that commit or we could change the all the remaining GFP_NOIOs in drivers/md/dm.c to "bio_opf & REQ_NOWAIT ? GFP_NOWAIT : GFP_NOIO". I'm not sure which one of these possibilities is better. Converting GFP_NOIOs would complicate dm.c a bit, but it would make sure that requests with REQ_NOWAIT don't really sleep. What do you think? Mikulas -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel