On Mon, May 25, 2020 at 08:10:27AM -0600, Jens Axboe wrote: > On 5/25/20 7:45 AM, Stefano Garzarella wrote: > > On Mon, May 25, 2020 at 12:30:51PM +0200, Stefano Garzarella wrote: > >> Hi Jens, > >> using fio and io_uring engine with SQPOLL and IOPOLL enabled, I had the > >> following issue that happens after 4/5 seconds fio has started. > >> Initially I had this issue on Linux v5.7-rc6, but I just tried also > >> Linux v5.7-rc7: > >> > >> [ 75.343479] nvme nvme0: pci function 0000:04:00.0 > >> [ 75.355110] nvme nvme0: 16/0/15 default/read/poll queues > >> [ 75.364946] nvme0n1: p1 > >> [ 82.739285] BUG: kernel NULL pointer dereference, address: 00000000000003b0 > >> [ 82.747054] #PF: supervisor read access in kernel mode > >> [ 82.752785] #PF: error_code(0x0000) - not-present page > >> [ 82.758516] PGD 800000046c042067 P4D 800000046c042067 PUD 461fcf067 PMD 0 > >> [ 82.766186] Oops: 0000 [#1] SMP PTI > >> [ 82.770076] CPU: 2 PID: 1307 Comm: io_uring-sq Not tainted 5.7.0-rc7 #11 > >> [ 82.777939] Hardware name: Dell Inc. PowerEdge R430/03XKDV, BIOS 1.2.6 06/08/2015 > >> [ 82.786290] RIP: 0010:task_numa_work+0x4f/0x2c0 > >> [ 82.791341] Code: 18 4c 8b 25 e3 f0 8e 01 49 8b 9f 00 08 00 00 4d 8b af c8 00 00 00 49 39 c7 0f 85 e8 01 00 00 48 89 6d 00 41 f6 47 24 04 75 67 <48> 8b ab b0 03 00 00 48 85 ed 75 16 8b 3d 6f 68 94 01 e8 aa fb 04 > >> [ 82.812296] RSP: 0018:ffffaaa98415be10 EFLAGS: 00010246 > >> [ 82.818123] RAX: ffff953ee36b8000 RBX: 0000000000000000 RCX: 0000000000000000 > >> [ 82.826083] RDX: 0000000000000001 RSI: ffff953ee36b8000 RDI: ffff953ee36b8dc8 > >> [ 82.834042] RBP: ffff953ee36b8dc8 R08: 00000000001200db R09: ffff9542e3ad2e08 > >> [ 82.842002] R10: ffff9542ecd20070 R11: 0000000000000000 R12: 00000000fffca35b > >> [ 82.849962] R13: 000000012a06a949 R14: ffff9542e3ad2c00 R15: ffff953ee36b8000 > >> [ 82.857922] FS: 0000000000000000(0000) GS:ffff953eefc40000(0000) knlGS:0000000000000000 > >> [ 82.866948] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > >> [ 82.873357] CR2: 00000000000003b0 CR3: 000000046bbd0002 CR4: 00000000001606e0 > >> [ 82.881316] Call Trace: > >> [ 82.884046] task_work_run+0x68/0xa0 > >> [ 82.888026] io_sq_thread+0x252/0x3d0 > >> [ 82.892111] ? finish_wait+0x80/0x80 > >> [ 82.896097] kthread+0xf9/0x130 > >> [ 82.899598] ? __ia32_sys_io_uring_enter+0x370/0x370 > >> [ 82.905134] ? kthread_park+0x90/0x90 > >> [ 82.909217] ret_from_fork+0x35/0x40 > >> [ 82.913203] Modules linked in: nvme nvme_core xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_reject_ipv4 tun bridge stp llc ip6table_mangle ip6table_nat iptable_mangle iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter rfkill sunrpc intel_rapl_msr intel_rapl_common sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul iTCO_wdt crc32_pclmul dcdbas ghash_clmulni_intel iTCO_vendor_support intel_cstate intel_uncore pcspkr intel_rapl_perf ipmi_ssif ixgbe mei_me mdio tg3 dca mei lpc_ich ipmi_si acpi_power_meter ipmi_devintf ipmi_msghandler ip_tables xfs libcrc32c mgag200 drm_kms_helper drm_vram_helper drm_ttm_helper ttm drm megaraid_sas crc32c_intel i2c_algo_bit wmi > >> [ 82.990613] CR2: 00000000000003b0 > >> [ 82.994307] ---[ end trace 6d1725e8f60fece7 ]--- > >> [ 83.039157] RIP: 0010:task_numa_work+0x4f/0x2c0 > >> [ 83.044211] Code: 18 4c 8b 25 e3 f0 8e 01 49 8b 9f 00 08 00 00 4d 8b af c8 00 00 00 49 39 c7 0f 85 e8 01 00 00 48 89 6d 00 41 f6 47 24 04 75 67 <48> 8b ab b0 03 00 00 48 85 ed 75 16 8b 3d 6f 68 94 01 e8 aa fb 04 > >> [ 83.065165] RSP: 0018:ffffaaa98415be10 EFLAGS: 00010246 > >> [ 83.070993] RAX: ffff953ee36b8000 RBX: 0000000000000000 RCX: 0000000000000000 > >> [ 83.078953] RDX: 0000000000000001 RSI: ffff953ee36b8000 RDI: ffff953ee36b8dc8 > >> [ 83.086913] RBP: ffff953ee36b8dc8 R08: 00000000001200db R09: ffff9542e3ad2e08 > >> [ 83.094873] R10: ffff9542ecd20070 R11: 0000000000000000 R12: 00000000fffca35b > >> [ 83.102833] R13: 000000012a06a949 R14: ffff9542e3ad2c00 R15: ffff953ee36b8000 > >> [ 83.110793] FS: 0000000000000000(0000) GS:ffff953eefc40000(0000) knlGS:0000000000000000 > >> [ 83.119821] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > >> [ 83.126230] CR2: 00000000000003b0 CR3: 000000046bbd0002 CR4: 00000000001606e0 > >> [ 113.113624] nvme nvme0: I/O 219 QID 19 timeout, aborting > >> [ 113.120135] nvme nvme0: Abort status: 0x0 > >> > >> Steps I did: > >> > >> $ modprobe nvme poll_queues=15 > >> $ fio fio_iou.job > >> > >> This is the fio_iou.job that I used: > >> > >> [global] > >> filename=/dev/nvme0n1 > >> ioengine=io_uring > >> direct=1 > >> runtime=60 > >> ramp_time=5 > >> gtod_reduce=1 > >> > >> cpus_allowed=4 > >> > >> [job1] > >> rw=randread > >> bs=4K > >> iodepth=1 > >> registerfiles > >> sqthread_poll=1 > >> sqthread_poll_cpu=2 > >> hipri > >> > >> I'll try to bisect, but I have some suspicions about: > >> b41e98524e42 io_uring: add per-task callback handler > > > > I confirm, the bisection ended with this: > > b41e98524e424d104aa7851d54fd65820759875a is the first bad commit > > I think the odd part here is that task_tick_numa() checks for a > valid mm, and queues work if the task has it. But for the sqpoll > kthread, the mm can come and go. By the time the task work is run, > the mm is gone and we oops on current->mm == NULL. > > I think the below should fix it: > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 538ba5d94e99..24a8557f001f 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2908,7 +2908,8 @@ static void task_tick_numa(struct rq *rq, struct task_struct *curr) > /* > * We don't care about NUMA placement if we don't have memory. > */ > - if (!curr->mm || (curr->flags & PF_EXITING) || work->next != work) > + if (!curr->mm || (curr->flags & (PF_EXITING | PF_KTHREAD)) || > + work->next != work) > return; > > /* > Great Jens! With this patch applied, everything works properly! Pavel, Hillf, thanks both for the comments, this patch solves the problem I have described. Thanks, Stefano
