• Jens Axboe's avatar
    blk-mq: fix discard merge with scheduler attached · 445251d0
    Jens Axboe authored
    I ran into an issue on my laptop that triggered a bug on the
    discard path:
    WARNING: CPU: 2 PID: 207 at drivers/nvme/host/core.c:527 nvme_setup_cmd+0x3d3/0x430
     Modules linked in: rfcomm fuse ctr ccm bnep arc4 binfmt_misc snd_hda_codec_hdmi nls_iso8859_1 nls_cp437 vfat snd_hda_codec_conexant fat snd_hda_codec_generic iwlmvm snd_hda_intel snd_hda_codec snd_hwdep mac80211 snd_hda_core snd_pcm snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq x86_pkg_temp_thermal intel_powerclamp kvm_intel uvcvideo iwlwifi btusb snd_seq_device videobuf2_vmalloc btintel videobuf2_memops kvm snd_timer videobuf2_v4l2 bluetooth irqbypass videobuf2_core aesni_intel aes_x86_64 crypto_simd cryptd snd glue_helper videodev cfg80211 ecdh_generic soundcore hid_generic usbhid hid i915 psmouse e1000e ptp pps_core xhci_pci xhci_hcd intel_gtt
     CPU: 2 PID: 207 Comm: jbd2/nvme0n1p7- Tainted: G     U           4.15.0+ #176
     Hardware name: LENOVO 20FBCTO1WW/20FBCTO1WW, BIOS N1FET59W (1.33 ) 12/19/2017
     RIP: 0010:nvme_setup_cmd+0x3d3/0x430
     RSP: 0018:ffff880423e9f838 EFLAGS: 00010217
     RAX: 0000000000000000 RBX: ffff880423e9f8c8 RCX: 0000000000010000
     RDX: ffff88022b200010 RSI: 0000000000000002 RDI: 00000000327f0000
     RBP: ffff880421251400 R08: ffff88022b200000 R09: 0000000000000009
     R10: 0000000000000000 R11: 0000000000000000 R12: 000000000000ffff
     R13: ffff88042341e280 R14: 000000000000ffff R15: ffff880421251440
     FS:  0000000000000000(0000) GS:ffff880441500000(0000) knlGS:0000000000000000
     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
     CR2: 000055b684795030 CR3: 0000000002e09006 CR4: 00000000001606e0
     DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
     DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
     Call Trace:
      ? __sbitmap_queue_get+0x24/0x90
      ? blk_mq_get_tag+0xa3/0x250
      ? wait_woken+0x80/0x80
      ? blk_mq_get_driver_tag+0x97/0xf0
      ? deadline_remove_request+0x49/0xb0
      ? submit_bio+0x5c/0x110
      ? __blkdev_issue_discard+0x152/0x200
      ? account_page_dirtied+0xe2/0x1a0
      ? kjournald2+0xb0/0x250
      ? wait_woken+0x80/0x80
      ? commit_timeout+0x10/0x10
      ? kthread_create_worker_on_cpu+0x50/0x50
      ? do_group_exit+0x3a/0xa0
     Code: 73 89 c1 83 ce 10 c1 e1 10 09 ca 83 f8 04 0f 87 0f ff ff ff 8b 4d 20 48 8b 7d 00 c1 e9 09 48 01 8c c7 00 08 00 00 e9 f8 fe ff ff <0f> ff 4c 89 c7 41 bc 0a 00 00 00 e8 0d 78 d6 ff e9 a1 fc ff ff
     ---[ end trace 50d361cc444506c8 ]---
     print_req_error: I/O error, dev nvme0n1, sector 847167488
    Decoding the assembly, the request claims to have 0xffff segments,
    while nvme counts two. This turns out to be because we don't check
    for a data carrying request on the mq scheduler path, and since
    blk_phys_contig_segment() returns true for a non-data request,
    we decrement the initial segment count of 0 and end up with
    0xffff in the unsigned short.
    There are a few issues here:
    1) We should initialize the segment count for a discard to 1.
    2) The discard merging is currently using the data limits for
       segments and sectors.
    Fix this up by having attempt_merge() correctly identify the
    request, and by initializing the segment count correctly
    for discards.
    This can only be triggered with mq-deadline on discard capable
    devices right now, which isn't a common configuration.
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>