Hi Keith, On 5/25/20 9:45 AM, Keith Busch wrote: > On Sun, May 24, 2020 at 07:33:02AM -0700, Dongli Zhang wrote: >>>> After code analysis, I think this is for nvme-pci as well. >>>> >>>> nvme_process_cq() >>>> -> nvme_handle_cqe() >>>> -> nvme_end_request() >>>> -> blk_mq_complete_request() >>>> nvme_reset_work() >>>> -> nvme_dev_disable() >>>> -> nvme_reap_pending_cqes() >>>> -> nvme_process_cq() >>>> -> nvme_handle_cqe() >>>> -> nvme_end_request() >>>> -> blk_mq_complete_request() >>>> -> __blk_mq_complete_request() >>>> -> __blk_mq_complete_request() >>> >>> nvme_dev_disable will first disable the queues before reaping the pending cqes so >>> it shouldn't have this issue. >>> >> >> Would you mind help explain how nvme_dev_disable() would avoid this issue? >> >> nvme_dev_disable() would: >> >> 1. freeze all the queues so that new request would not enter and submit >> 2. NOT wait for freezing during live reset so that q->q_usage_counter is not >> guaranteed to be zero. >> 3. quiesce all the queues so that new request would not dispatch >> 4. delete the queue and free irq >> >> However, I do not find a mechanism to prevent if a nvme_end_request() is already >> in progress. >> >> E.g., suppose __blk_mq_complete_request() is already triggered on cpu 3 and >> waiting for its first line "WRITE_ONCE(rq->state, MQ_RQ_COMPLETE)" to be >> executed ... while another cpu is doing live reset. I do not see how to prevent >> such race. > > The queues and their interrupts are torn and synchronized down before the reset > reclaims uncompleted requests. There's no other context that can be running > completions at that point. Thank you very much for the clarification. There are 3 cases for a nvme request to complete. 1. In the context of irq. While I did not test with source code, I think it is because nvme_suspend_queue()-->pci_free_irq() which would wait for all infligh IRQ handler with __synchronize_hardirq(). 2. In the context of irq thread when threaded irq is involved. The nvme_suspend_queue()-->pci_free_irq() would finally wait for the stop of irq thread by kthread_stop(action->thread). Therefore, there is not any IRQ handler running in kernel thread. 3. In the context of blk_poll(). I do not find a mechanism to protect the race in this case. By adding mdelay() to code, I am able to reproduce the below race on purpose. [ 235.223975] ================================================================== [ 235.224878] BUG: KASAN: null-ptr-deref in blk_mq_free_request+0x363/0x510 [ 235.225674] Write of size 4 at addr 0000000000000198 by task swapper/3/0 [ 235.226456] [ 235.226772] ================================================================== [ 235.227633] BUG: kernel NULL pointer dereference, address: 0000000000000198 [ 235.228447] #PF: supervisor write access in kernel mode [ 235.229062] #PF: error_code(0x0002) - not-present page [ 235.229667] PGD 0 P4D 0 [ 235.229976] Oops: 0002 [#1] SMP KASAN PTI [ 235.230451] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G B 5.7.0-rc5+ #1 [ 235.231347] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 [ 235.232692] RIP: 0010:blk_mq_free_request+0x367/0x510 [ 235.233286] Code: 89 df 5b 5d 41 5c 41 5d 41 5e 41 5f e9 a2 dc ff ff 48 8d ba 98 01 00 00 be 04 00 00 00 48 89 14 24 e8 fd 69 9a ff 48 8b 14 24 <f0> ff 8a 98 01 00 00 e9 e2 fe ff ff 48 83 c4 08 48 89 ef be 03 00 [ 235.235503] RSP: 0018:ffff8881f7389be0 EFLAGS: 00010046 [ 235.236114] RAX: 0000000000000000 RBX: ffff8881f21b9680 RCX: ffffffff816e05b1 [ 235.236941] RDX: 0000000000000000 RSI: 0000000000000046 RDI: 0000000000000046 [ 235.237770] RBP: 0000000000000001 R08: fffffbfff0af5869 R09: fffffbfff0af5869 [ 235.238598] R10: ffffffff857ac347 R11: fffffbfff0af5868 R12: ffff8881f21b969c [ 235.239424] R13: ffff8881f0f62738 R14: ffffe8ffffd884c0 R15: ffff8881f21b9698 [ 235.240255] FS: 0000000000000000(0000) GS:ffff8881f7380000(0000) knlGS:0000000000000000 [ 235.241192] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 235.241863] CR2: 0000000000000198 CR3: 00000001eb886004 CR4: 0000000000360ee0 [ 235.242695] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 235.243523] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 235.244349] Call Trace: [ 235.244645] <IRQ> [ 235.244890] blk_mq_complete_request+0x266/0x460 [ 235.245432] nvmet_req_complete+0xd/0xb0 [ 235.245898] iomap_dio_bio_end_io+0x336/0x480 [ 235.246409] blk_update_request+0x320/0x960 [ 235.246904] blk_mq_end_request+0x4e/0x4d0 [ 235.247391] blk_mq_complete_request+0x266/0x460 [ 235.247937] virtblk_done+0x164/0x300 [ 235.248372] ? loop_queue_work.cold.44+0x5e/0x5e [ 235.248915] ? rcu_accelerate_cbs+0x5d/0x1a70 [ 235.249429] ? virtqueue_get_used_addr+0x140/0x140 [ 235.249990] vring_interrupt+0x16d/0x280 [ 235.250454] __handle_irq_event_percpu+0xdd/0x470 [ 235.251010] handle_irq_event_percpu+0x6e/0x130 [ 235.251544] ? rcu_accelerate_cbs_unlocked+0x110/0x110 [ 235.252145] ? __handle_irq_event_percpu+0x470/0x470 [ 235.252729] ? _raw_spin_lock+0x75/0xd0 [ 235.253181] ? _raw_write_lock+0xd0/0xd0 [ 235.253645] handle_irq_event+0xc2/0x158 [ 235.254107] handle_edge_irq+0x1e9/0x7a0 [ 235.254572] do_IRQ+0x94/0x1e0 [ 235.254936] common_interrupt+0xf/0xf [ 235.255368] </IRQ> [ 235.255629] RIP: 0010:native_safe_halt+0xe/0x10 [ 235.256162] Code: e9 f2 fe ff ff 48 89 df e8 2f dc f8 fd eb a4 cc cc cc cc cc cc cc cc cc cc cc cc cc e9 07 00 00 00 0f 00 2d a4 7d 4a 00 fb f4 <c3> 90 e9 07 00 00 00 0f 00 2d 94 7d 4a 00 f4 c3 cc cc 41 56 41 55 [ 235.258314] RSP: 0018:ffff8881f61ffdd8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffffde [ 235.259194] RAX: ffffffff83bc59f0 RBX: dffffc0000000000 RCX: ffffffff83bc6639 [ 235.260022] RDX: 1ffff1103ec398e8 RSI: 0000000000000008 RDI: ffff8881f61cc740 [ 235.260850] RBP: 0000000000000003 R08: ffffed103ec398e9 R09: ffffed103ec398e9 [ 235.261681] R10: ffff8881f61cc747 R11: ffffed103ec398e8 R12: ffffffff84e5c4c0 [ 235.262508] R13: 0000000000000003 R14: 1ffff1103ec3ffc4 R15: 0000000000000000 [ 235.263338] ? __cpuidle_text_start+0x8/0x8 [ 235.263832] ? default_idle_call+0x29/0x60 [ 235.264315] ? tsc_verify_tsc_adjust+0x68/0x1f0 [ 235.264849] default_idle+0x1a/0x2b0 [ 235.265273] do_idle+0x2fd/0x3b0 [ 235.265658] ? arch_cpu_idle_exit+0x40/0x40 [ 235.266151] ? schedule_idle+0x56/0x90 [ 235.266595] cpu_startup_entry+0x14/0x20 [ 235.267057] start_secondary+0x2a6/0x340 [ 235.267522] ? set_cpu_sibling_map+0x1fb0/0x1fb0 [ 235.268066] secondary_startup_64+0xb6/0xc0 [ 235.268561] Modules linked in: [ 235.268929] CR2: 0000000000000198 [ 235.269330] ---[ end trace f8fa823705a3dbe7 ]--- [ 235.269875] RIP: 0010:blk_mq_free_request+0x367/0x510 [ 235.270466] Code: 89 df 5b 5d 41 5c 41 5d 41 5e 41 5f e9 a2 dc ff ff 48 8d ba 98 01 00 00 be 04 00 00 00 48 89 14 24 e8 fd 69 9a ff 48 8b 14 24 <f0> ff 8a 98 01 00 00 e9 e2 fe ff ff 48 83 c4 08 48 89 ef be 03 00 [ 235.272622] RSP: 0018:ffff8881f7389be0 EFLAGS: 00010046 [ 235.273230] RAX: 0000000000000000 RBX: ffff8881f21b9680 RCX: ffffffff816e05b1 [ 235.274063] RDX: 0000000000000000 RSI: 0000000000000046 RDI: 0000000000000046 [ 235.274890] RBP: 0000000000000001 R08: fffffbfff0af5869 R09: fffffbfff0af5869 [ 235.275717] R10: ffffffff857ac347 R11: fffffbfff0af5868 R12: ffff8881f21b969c [ 235.276545] R13: ffff8881f0f62738 R14: ffffe8ffffd884c0 R15: ffff8881f21b9698 [ 235.277371] FS: 0000000000000000(0000) GS:ffff8881f7380000(0000) knlGS:0000000000000000 [ 235.278307] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 235.278977] CR2: 0000000000000198 CR3: 00000001eb886004 CR4: 0000000000360ee0 [ 235.279805] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 235.280632] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 235.281459] Kernel panic - not syncing: Fatal exception in interrupt [ 235.282474] Kernel Offset: 0x400000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff) [ 235.283695] ---[ end Kernel panic - not syncing: Fatal exception in interrupt ]--- I have sent the below for feedback. https://lore.kernel.org/linux-nvme/20200527004955.19463-1-dongli.zhang@xxxxxxxxxx/T/#u Thank you very much! Dongli Zhang
