WARNING: CPU: 2 PID: 207 at drivers/nvme/host/core.c:527 nvme_setup_cmd+0x3d3

[jianchao.wang]

Hi Jens

On 01/30/2018 11:57 PM, Jens Axboe wrote:
> On 1/30/18 8:41 AM, Jens Axboe wrote:
>> Hi,
>>
>> I just hit this on 4.15+ on the laptop, it's running Linus' git
>> as of yesterday, right after the block tree merge:
>>
>> commit 0a4b6e2f80aad46fb55a5cf7b1664c0aef030ee0
>> Merge: 9697e9da8429 796baeeef85a
>> Author: Linus Torvalds <torvalds at linux-foundation.org>
>> Date:   Mon Jan 29 11:51:49 2018 -0800
>>
>>     Merge branch 'for-4.16/block' of git://git.kernel.dk/linux-block
>>
>> It's hitting this case:
>>
>>         if (WARN_ON_ONCE(n != segments)) {                                      
>>
>> in nvme, indicating that rq->nr_phys_segments does not equal the
>> number of bios in the request. Anyone seen this? I'll take a closer
>> look as time permits, full trace below.
>>
>>
>>  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:
>>   nvme_queue_rq+0x40/0xa00
>>   ? __sbitmap_queue_get+0x24/0x90
>>   ? blk_mq_get_tag+0xa3/0x250
>>   ? wait_woken+0x80/0x80
>>   ? blk_mq_get_driver_tag+0x97/0xf0
>>   blk_mq_dispatch_rq_list+0x7b/0x4a0
>>   ? deadline_remove_request+0x49/0xb0
>>   blk_mq_do_dispatch_sched+0x4f/0xc0
>>   blk_mq_sched_dispatch_requests+0x106/0x170
>>   __blk_mq_run_hw_queue+0x53/0xa0
>>   __blk_mq_delay_run_hw_queue+0x83/0xa0
>>   blk_mq_run_hw_queue+0x6c/0xd0
>>   blk_mq_sched_insert_request+0x96/0x140
>>   __blk_mq_try_issue_directly+0x3d/0x190
>>   blk_mq_try_issue_directly+0x30/0x70
>>   blk_mq_make_request+0x1a4/0x6a0
>>   generic_make_request+0xfd/0x2f0
>>   ? submit_bio+0x5c/0x110
>>   submit_bio+0x5c/0x110
>>   ? __blkdev_issue_discard+0x152/0x200
>>   submit_bio_wait+0x43/0x60
>>   ext4_process_freed_data+0x1cd/0x440
>>   ? account_page_dirtied+0xe2/0x1a0
>>   ext4_journal_commit_callback+0x4a/0xc0
>>   jbd2_journal_commit_transaction+0x17e2/0x19e0
>>   ? kjournald2+0xb0/0x250
>>   kjournald2+0xb0/0x250
>>   ? wait_woken+0x80/0x80
>>   ? commit_timeout+0x10/0x10
>>   kthread+0x111/0x130
>>   ? kthread_create_worker_on_cpu+0x50/0x50
>>   ? do_group_exit+0x3a/0xa0
>>   ret_from_fork+0x1f/0x30
>>  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
> 
> Looking at the disassembly, 'n' is 2 and 'segments' is 0xffff.
> 

Let's consider the case following:

blk_mq_bio_to_request()
  -> blk_init_request_from_bio()
    -> blk_rq_bio_prep()
    ----
    if (bio_has_data(bio))
        rq->nr_phys_segments = bio_phys_segments(q, bio);
    ----
static inline bool bio_has_data(struct bio *bio)
{
    if (bio &&
        bio->bi_iter.bi_size &&
        bio_op(bio) != REQ_OP_DISCARD &&   //-----> HERE !
        bio_op(bio) != REQ_OP_SECURE_ERASE &&
        bio_op(bio) != REQ_OP_WRITE_ZEROES)
        return true;

    return false;
}
For the DISCARD req, the nr_phys_segments is 0.

dd_insert_request()
  -> blk_mq_sched_try_insert_merge()
    -> elv_attempt_insert_merge()
      -> blk_attempt_req_merge()
        -> attempt_merge()
          -> ll_merge_requests_fn()
----
    total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
    // total_phys_segments will be 0
    if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
        if (req->nr_phys_segments == 1)
            req->bio->bi_seg_front_size = seg_size;
        if (next->nr_phys_segments == 1)
            next->biotail->bi_seg_back_size = seg_size;
        // total_phys_segments is int, it will be -1;
        total_phys_segments--;
    }

    //total_phys_segments is -1, so it is false here
    if (total_phys_segments > queue_max_segments(q))
        return 0;

    if (blk_integrity_merge_rq(q, req, next) == false)
        return 0;

    /* Merge is OK... */
    // -1 is set to req->nr_phys_segments which is a unsigned short
    // finally, we get a 0xffff
    req->nr_phys_segments = total_phys_segments;
----

Thanks
Jianchao