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SubjectRe: usercopy whitelist woe in scsi_sense_cache
Hi.

(fancy details for linux-block and BFQ people go below)

09.04.2018 20:32, Kees Cook wrote:
> Ah, this detail I didn't have. I've changed my environment to
>
> build with:
>
> CONFIG_BLK_MQ_PCI=y
> CONFIG_BLK_MQ_VIRTIO=y
> CONFIG_IOSCHED_BFQ=y
>
> boot with scsi_mod.use_blk_mq=1
>
> and select BFQ in the scheduler:
>
> # cat /sys/block/sd?/queue/scheduler
> mq-deadline kyber [bfq] none
> mq-deadline kyber [bfq] none
>
> Even with this, I'm not seeing anything yet...

Thanks for looking into it anyway. I was experimenting today a little
bit, and for me it looks like setting queue_depth and nr_requests to
minimal values speeds up the reproducing. Could you please try it too?
Something like:

echo 1 | tee /sys/block/sd*/queue/nr_requests
echo 1 | tee /sys/block/sd*/device/queue_depth

Also, now I have a more solid proof that this is related to I/O
scheduling.

I was hammering my VM, and after a couple of usercopy warnings/bugs I
can reliably trigger I/O hang. I was able to obtain the stack traces of
tasks in D state. Listing them here below. dmcrypt_write:

===
[ 1615.409622] dmcrypt_write D 0 236 2 0x80000000
[ 1615.413422] Call Trace:
[ 1615.415428] ? __schedule+0x336/0xf40
[ 1615.417824] ? blk_mq_sched_dispatch_requests+0x117/0x190
[ 1615.421423] ? __sbitmap_get_word+0x2a/0x80
[ 1615.424202] schedule+0x32/0xc0
[ 1615.426521] io_schedule+0x12/0x40
[ 1615.432414] blk_mq_get_tag+0x181/0x2a0
[ 1615.434881] ? elv_merge+0x79/0xe0
[ 1615.437447] ? wait_woken+0x80/0x80
[ 1615.439553] blk_mq_get_request+0xf9/0x400
[ 1615.444653] blk_mq_make_request+0x10b/0x640
[ 1615.448025] generic_make_request+0x124/0x2d0
[ 1615.450716] ? raid10_unplug+0xfb/0x180 [raid10]
[ 1615.454069] raid10_unplug+0xfb/0x180 [raid10]
[ 1615.456729] blk_flush_plug_list+0xc1/0x250
[ 1615.460276] blk_finish_plug+0x27/0x40
[ 1615.464103] dmcrypt_write+0x233/0x240 [dm_crypt]
[ 1615.467443] ? wake_up_process+0x20/0x20
[ 1615.470845] ? crypt_iv_essiv_dtr+0x60/0x60 [dm_crypt]
[ 1615.475272] ? kthread+0x113/0x130
[ 1615.477652] kthread+0x113/0x130
[ 1615.480567] ? kthread_create_on_node+0x70/0x70
[ 1615.483268] ret_from_fork+0x35/0x40
===

One of XFS threads, too:

===
[ 1616.133298] xfsaild/dm-7 D 0 316 2 0x80000000
[ 1616.136679] Call Trace:
[ 1616.138845] ? __schedule+0x336/0xf40
[ 1616.141581] ? preempt_count_add+0x68/0xa0
[ 1616.147214] ? _raw_spin_unlock+0x16/0x30
[ 1616.149813] ? _raw_spin_unlock_irqrestore+0x20/0x40
[ 1616.152478] ? try_to_del_timer_sync+0x4d/0x80
[ 1616.154734] schedule+0x32/0xc0
[ 1616.156579] _xfs_log_force+0x146/0x290 [xfs]
[ 1616.159322] ? wake_up_process+0x20/0x20
[ 1616.162175] xfsaild+0x1a9/0x820 [xfs]
[ 1616.164695] ? xfs_trans_ail_cursor_first+0x80/0x80 [xfs]
[ 1616.167567] ? kthread+0x113/0x130
[ 1616.169722] kthread+0x113/0x130
[ 1616.171908] ? kthread_create_on_node+0x70/0x70
[ 1616.174073] ? do_syscall_64+0x74/0x190
[ 1616.179008] ? SyS_exit_group+0x10/0x10
[ 1616.182306] ret_from_fork+0x35/0x40
===

journald is another victim:

===
[ 1616.184343] systemd-journal D 0 354 1 0x00000104
[ 1616.187282] Call Trace:
[ 1616.189464] ? __schedule+0x336/0xf40
[ 1616.191781] ? call_function_single_interrupt+0xa/0x20
[ 1616.194788] ? _raw_spin_lock_irqsave+0x25/0x50
[ 1616.197592] schedule+0x32/0xc0
[ 1616.200171] schedule_timeout+0x202/0x470
[ 1616.202851] ? preempt_count_add+0x49/0xa0
[ 1616.206227] wait_for_common+0xbb/0x180
[ 1616.209877] ? wake_up_process+0x20/0x20
[ 1616.212511] do_coredump+0x335/0xea0
[ 1616.214861] ? schedule+0x3c/0xc0
[ 1616.216775] ? futex_wait_queue_me+0xbb/0x110
[ 1616.218894] ? _raw_spin_unlock+0x16/0x30
[ 1616.220868] ? futex_wait+0x143/0x240
[ 1616.223450] get_signal+0x250/0x5c0
[ 1616.225965] do_signal+0x36/0x610
[ 1616.228246] ? __seccomp_filter+0x3b/0x260
[ 1616.231000] ? __check_object_size+0x9f/0x1a0
[ 1616.233716] exit_to_usermode_loop+0x85/0xa0
[ 1616.238413] do_syscall_64+0x18b/0x190
[ 1616.240798] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ 1616.244401] RIP: 0033:0x7f78fc53e45d
[ 1616.246690] RSP: 002b:00007ffd40330d20 EFLAGS: 00000246 ORIG_RAX:
00000000000000ca
[ 1616.251199] RAX: fffffffffffffe00 RBX: 00007f78f7806700 RCX:
00007f78fc53e45d
[ 1616.254817] RDX: 00000000000004cd RSI: 0000000000000000 RDI:
00007f78f78069d0
[ 1616.258410] RBP: 00007ffd40330d20 R08: 00000000000000ca R09:
00007f78f78069d0
[ 1616.261813] R10: 0000000000000000 R11: 0000000000000246 R12:
0000000000000000
[ 1616.265065] R13: 0000000000000000 R14: 00007f78fc95e8c0 R15:
00007f78f7806d28

[ 1616.272861] journal-offline D 0 1229 1 0x00000104
[ 1616.275856] Call Trace:
[ 1616.277396] ? __schedule+0x336/0xf40
[ 1616.279258] ? release_pages+0x192/0x3d0
[ 1616.282871] schedule+0x32/0xc0
[ 1616.285218] io_schedule+0x12/0x40
[ 1616.287267] wait_on_page_bit+0xea/0x130
[ 1616.291084] ? add_to_page_cache_lru+0xe0/0xe0
[ 1616.293898] __filemap_fdatawait_range+0xbb/0x110
[ 1616.297391] ? xen_swiotlb_init+0x85/0x4d0
[ 1616.303285] file_write_and_wait_range+0x76/0xa0
[ 1616.306313] xfs_file_fsync+0x5d/0x240 [xfs]
[ 1616.309196] ? syscall_trace_enter+0xd8/0x2d0
[ 1616.312193] do_fsync+0x38/0x60
[ 1616.314654] SyS_fsync+0xc/0x10
[ 1616.318686] do_syscall_64+0x74/0x190
[ 1616.321519] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ 1616.324045] RIP: 0033:0x7f78fc5470ec
[ 1616.326257] RSP: 002b:00007f78f7805d30 EFLAGS: 00000293 ORIG_RAX:
000000000000004a
[ 1616.333535] RAX: ffffffffffffffda RBX: 00005597340357b0 RCX:
00007f78fc5470ec
[ 1616.337057] RDX: 0000000000000000 RSI: 00007f78fbea3811 RDI:
0000000000000013
[ 1616.341176] RBP: 00007f78fbea4c60 R08: 00007f78f7806700 R09:
00007f78f7806700
[ 1616.345029] R10: 0000000000000811 R11: 0000000000000293 R12:
0000000000000002
[ 1616.349279] R13: 00007ffd40330e8f R14: 00007ffd40330e90 R15:
0000000000000016

[ 1876.568670] systemd-journal D 0 14892 1 0x00000100
[ 1876.573395] Call Trace:
[ 1876.575559] ? __schedule+0x336/0xf40
[ 1876.578005] ? memcg_kmem_charge+0xad/0xf0
[ 1876.580797] ? lock_page_memcg+0x11/0x80
[ 1876.583674] schedule+0x32/0xc0
[ 1876.585516] io_schedule+0x12/0x40
[ 1876.590223] wait_on_page_bit+0xea/0x130
[ 1876.591840] ? add_to_page_cache_lru+0xe0/0xe0
[ 1876.593554] __filemap_fdatawait_range+0xbb/0x110
[ 1876.595340] ? store_online+0x34/0xb0
[ 1876.596913] ? __filemap_fdatawrite_range+0xc1/0x100
[ 1876.599338] ? __filemap_fdatawrite_range+0xcf/0x100
[ 1876.601447] file_write_and_wait_range+0x76/0xa0
[ 1876.604356] xfs_file_fsync+0x5d/0x240 [xfs]
[ 1876.606599] ? syscall_trace_enter+0xd8/0x2d0
[ 1876.608753] do_fsync+0x38/0x60
[ 1876.610952] SyS_fsync+0xc/0x10
[ 1876.612442] do_syscall_64+0x74/0x190
[ 1876.615383] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ 1876.622030] RIP: 0033:0x7fe056a840c4
[ 1876.624698] RSP: 002b:00007ffe7908ce88 EFLAGS: 00000246 ORIG_RAX:
000000000000004a
[ 1876.628290] RAX: ffffffffffffffda RBX: 000055ad65d1f9c0 RCX:
00007fe056a840c4
[ 1876.630922] RDX: 00007fe0563e1c7c RSI: 0000000000000003 RDI:
0000000000000017
[ 1876.634244] RBP: 00007fe0563e1c60 R08: 0000000000000005 R09:
0000000000000002
[ 1876.637153] R10: 000055ad65d1a010 R11: 0000000000000246 R12:
0000000000000002
[ 1876.640099] R13: 00000000fffffff0 R14: 0000000000000002 R15:
00007ffe7908d2e0
===

And what's more important, I can make smartctl hang too!

===
[ 1876.466385] smartctl D 0 14891 495 0x00000000
[ 1876.469100] Call Trace:
[ 1876.471267] ? __schedule+0x336/0xf40
[ 1876.473541] ? blk_mq_sched_dispatch_requests+0x117/0x190
[ 1876.476331] ? __sbitmap_get_word+0x2a/0x80
[ 1876.478784] ? sbitmap_get_shallow+0x5c/0xa0
[ 1876.481353] schedule+0x32/0xc0
[ 1876.484412] io_schedule+0x12/0x40
[ 1876.486892] blk_mq_get_tag+0x181/0x2a0
[ 1876.489448] ? wait_woken+0x80/0x80
[ 1876.492018] blk_mq_get_request+0xf9/0x400
[ 1876.497734] ? lookup_fast+0xc8/0x2d0
[ 1876.501050] blk_mq_alloc_request+0x7e/0xe0
[ 1876.503705] blk_get_request_flags+0x40/0x160
[ 1876.506306] sg_io+0x9d/0x3f0
[ 1876.507920] ? path_lookupat+0xaa/0x1f0
[ 1876.509750] ? current_time+0x18/0x70
[ 1876.511496] scsi_cmd_ioctl+0x257/0x410
[ 1876.513151] ? xfs_bmapi_read+0x1c3/0x340 [xfs]
[ 1876.515355] sd_ioctl+0xbf/0x1a0 [sd_mod]
[ 1876.517638] blkdev_ioctl+0x8ca/0x990
[ 1876.519219] ? read_null+0x10/0x10
[ 1876.520849] block_ioctl+0x39/0x40
[ 1876.522368] do_vfs_ioctl+0xa4/0x630
[ 1876.524490] ? vfs_write+0x164/0x1a0
[ 1876.526841] SyS_ioctl+0x74/0x80
[ 1876.528328] do_syscall_64+0x74/0x190
[ 1876.529886] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[ 1876.537471] RIP: 0033:0x7f4f232c8d87
[ 1876.540388] RSP: 002b:00007ffd0fe530a8 EFLAGS: 00000246 ORIG_RAX:
0000000000000010
[ 1876.545738] RAX: ffffffffffffffda RBX: 00007ffd0fe53350 RCX:
00007f4f232c8d87
[ 1876.548950] RDX: 00007ffd0fe530c0 RSI: 0000000000002285 RDI:
0000000000000003
[ 1876.552912] RBP: 00007ffd0fe533a0 R08: 0000000000000010 R09:
00007ffd0fe53980
[ 1876.559750] R10: 0000000000000200 R11: 0000000000000246 R12:
000055e98902dce0
[ 1876.563829] R13: 0000000000000000 R14: 000055e989027550 R15:
00000000000000d0
===

Workqueues, also from alt+sysrq+t dump:

===
[ 1876.676508] Showing busy workqueues and worker pools:
[ 1876.681916] workqueue events_power_efficient: flags=0x82
[ 1876.685388] pwq 8: cpus=0-3 flags=0x4 nice=0 active=2/256
[ 1876.688962] pending: fb_flashcursor, neigh_periodic_work
[ 1876.694414] workqueue events_freezable_power_: flags=0x86
[ 1876.699262] pwq 8: cpus=0-3 flags=0x4 nice=0 active=1/256
[ 1876.703777] pending: disk_events_workfn
[ 1876.707279] workqueue dm-thin: flags=0xa000a
[ 1876.709053] pwq 8: cpus=0-3 flags=0x4 nice=0 active=1/1
[ 1876.715598] pending: do_waker [dm_thin_pool]
===

So far, I can reproduce it only with blk-mq *and* BFQ enabled. I've
switched another machine (my server) to Kyber, and I do not observe the
issue (so far, at least).

Paolo, Jens? I don't know whom to address, actually :(. Can someone give
me an idea on this please?

> The thing I can't figure out is how req->sense is slipping forward in
> (and even beyond!) the allocation.

*cough* race condition *cough* ☺

Regards,
Oleksandr

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