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Fri, 15 Sep 2023 09:14:24 -0700 (PDT) Received: from [192.168.1.94] ([96.43.243.2]) by smtp.gmail.com with ESMTPSA id b4-20020a920b04000000b003459023deaasm1203235ilf.30.2023.09.15.09.14.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Sep 2023 09:14:24 -0700 (PDT) Message-ID: <514767b4-5b2a-4f8e-a6ba-6722ddac5330@kernel.dk> Date: Fri, 15 Sep 2023 10:14:23 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Jens Axboe To: Mike Snitzer , "dm-devel@redhat.com" , Mikulas Patocka References: <4f5737f0-9299-4968-8cb5-07c7645bbffd@kernel.dk> In-Reply-To: <4f5737f0-9299-4968-8cb5-07c7645bbffd@kernel.dk> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false 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: , Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: kernel.dk Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit 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. -- Jens Axboe -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel