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Subject: Re: [LKP] a9f38e1dec [ 245.678853] INFO: task mount:580 blocked for
 more than 120 seconds.
To:     "jianchao.wang" <jianchao.w.wang@oracle.com>,
        kernel test robot <rong.a.chen@intel.com>,
        Omar Sandoval <osandov@fb.com>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        LKP <lkp@01.org>
References: <20181107031643.GD24195@shao2-debian>
 <f5f81267-0aea-4ae1-0112-88279598eb07@oracle.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <1de09da9-fc06-b26e-99fa-97d813c0ccf0@kernel.dk>
Date:   Wed, 7 Nov 2018 08:17:43 -0700
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On 11/7/18 1:22 AM, jianchao.wang wrote:
> 
> 
> On 11/7/18 11:16 AM, kernel test robot wrote:
>> Greetings,
>>
>> 0day kernel testing robot got the below dmesg and the first bad commit is
>>
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_torvalds_linux.git&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=7WdAxUBeiTUTCy8v-7zXyr4qk7sx26ATvfo6QSTvZyQ&m=8qsZc_c8QfZOGoITiebvlt5BO9GBK61cAY4xLOCegFU&s=ZGRhkdRCPvSKvbZzx-HAQtWcDZfzce60e2TMvBQyORo&e= master
>>
>> commit a9f38e1dec107af70d81338332494bf0a1e76597
>> Author:     Omar Sandoval <osandov@fb.com>
>> AuthorDate: Mon Oct 15 09:21:34 2018 -0600
>> Commit:     Jens Axboe <axboe@kernel.dk>
>> CommitDate: Tue Oct 16 09:50:14 2018 -0600
>>
>>     floppy: convert to blk-mq
>>     
>>     This driver likes to fetch requests from all over the place, so make
>>     queue_rq put requests on a list so that the logic stays the same. Tested
>>     with QEMU.
>>     
>>     Signed-off-by: Omar Sandoval <osandov@fb.com>
>>     
>>     Converted to blk_mq_init_sq_queue() and fixed a few spots where the
>>     tag_set leaked on cleanup.
>>     
>>     Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> 6ec3938cff  ataflop: convert to blk-mq
>> a9f38e1dec  floppy: convert to blk-mq
>> 8053e5b93e  Merge tag 'trace-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace
>> 337734cbca  Add linux-next specific files for 20181106
>> +---------------------------------------------------------+------------+------------+------------+---------------+
>> |                                                         | 6ec3938cff | a9f38e1dec | 8053e5b93e | next-20181106 |
>> +---------------------------------------------------------+------------+------------+------------+---------------+
>> | boot_successes                                          | 251        | 68         | 69         | 74            |
>> | boot_failures                                           | 48         | 27         | 25         | 23            |
>> | Mem-Info                                                | 48         | 12         | 15         | 7             |
>> | invoked_oom-killer:gfp_mask=0x                          | 6          | 4          | 3          | 2             |
>> | EIP:iov_iter_fault_in_readable                          | 4          | 1          |            |               |
>> | Out_of_memory:Kill_process                              | 3          | 2          | 2          |               |
>> | Out_of_memory_and_no_killable_processes                 | 3          | 2          | 2          |               |
>> | Kernel_panic-not_syncing:System_is_deadlocked_on_memory | 3          | 2          | 2          |               |
>> | EIP:__put_user_4                                        | 1          |            |            |               |
>> | INFO:task_blocked_for_more_than#seconds                 | 0          | 15         | 10         | 16            |
>> | EIP:lock_is_held_type                                   | 0          | 1          | 0          | 1             |
>> | EIP:native_safe_halt                                    | 0          | 3          |            |               |
>> | Kernel_panic-not_syncing:hung_task:blocked_tasks        | 0          | 15         | 10         | 16            |
>> | EIP:strnlen_user                                        | 0          | 1          |            |               |
>> | EIP:_local_bh_enable                                    | 0          | 1          |            |               |
>> | EIP:__lock_acquire                                      | 0          | 1          | 1          | 1             |
>> | EIP:vprintk_emit                                        | 0          | 1          |            |               |
>> | EIP:do_softirq_own_stack                                | 0          | 0          | 1          |               |
>> | EIP:default_idle                                        | 0          | 0          | 2          | 1             |
>> | EIP:reschedule_interrupt                                | 0          | 0          | 1          |               |
>> | EIP:delay_tsc                                           | 0          | 0          | 0          | 1             |
>> | EIP:copy_page_from_iter                                 | 0          | 0          | 0          | 1             |
>> | EIP:_cond_resched                                       | 0          | 0          | 0          | 1             |
>> +---------------------------------------------------------+------------+------------+------------+---------------+
>>
>> [  244.196551] random: get_random_u32 called from arch_align_stack+0x2d/0x40 with crng_init=1
>> [  245.254485] _warn_unseeded_randomness: 54 callbacks suppressed
>> [  245.254491] random: get_random_u32 called from copy_process+0x1c8/0x17b0 with crng_init=1
>> [  245.257366] random: get_random_u32 called from arch_pick_mmap_layout+0x110/0x140 with crng_init=1
>> [  245.258675] random: get_random_u32 called from load_elf_binary+0x2b6/0xb48 with crng_init=1
>> [  245.678853] INFO: task mount:580 blocked for more than 120 seconds.
>> [  245.679906]       Tainted: G                T 4.19.0-rc6-00172-ga9f38e1 #1
>> [  245.680959] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [  245.682181] mount           D 6372   580      1 0x00000004
>> [  245.683023] Call Trace:
>> [  245.683425]  __schedule+0x2df/0x570
>> [  245.683975]  schedule+0x2d/0x80
>> [  245.684476]  schedule_timeout+0x19d/0x330
>> [  245.685090]  ? wait_for_common+0xa5/0x170
>> [  245.685735]  wait_for_common+0xac/0x170
>> [  245.686339]  ? do_sched_yield+0x90/0x90
>> [  245.686935]  wait_for_completion+0x12/0x20
>> [  245.687571]  __floppy_read_block_0+0xfb/0x150
>> [  245.688244]  ? floppy_resume+0x40/0x40
>> [  245.688844]  floppy_revalidate+0x20f/0x240
>> [  245.689486]  check_disk_change+0x43/0x60
>> [  245.690087]  floppy_open+0x1ea/0x360
>> [  245.690653]  __blkdev_get+0xb4/0x4d0
>> [  245.691212]  ? blkdev_get+0x1db/0x370
>> [  245.691777]  blkdev_get+0x1f3/0x370
>> [  245.692351]  ? path_put+0x15/0x20
>> [  245.692871]  ? lookup_bdev+0x4b/0x90
>> [  245.693539]  blkdev_get_by_path+0x3d/0x80
>> [  245.694165]  mount_bdev+0x2a/0x190
>> [  245.694695]  squashfs_mount+0x10/0x20
>> [  245.695271]  ? squashfs_alloc_inode+0x30/0x30
>> [  245.695960]  mount_fs+0xf/0x90
>> [  245.696451]  vfs_kern_mount+0x43/0x130
>> [  245.697036]  do_mount+0x187/0xc40
>> [  245.697563]  ? memdup_user+0x28/0x50
>> [  245.698124]  ksys_mount+0x60/0xc0
>> [  245.698639]  sys_mount+0x19/0x20
>> [  245.699167]  do_int80_syscall_32+0x61/0x130
>> [  245.699813]  entry_INT80_32+0xc7/0xc7
>> [  245.700391] EIP: 0x47f46fee
>> [  245.700829] Code: 11 83 c8 ff eb e2 90 90 90 90 90 90 57 56 53 8b 7c 24 20 8b 74 24 1c 8b 54 24 18 8b 4c 24 14 8b 5c 24 10 b8 15 00 00 00 cd 80 <5b> 5e 5f 3d 01 f0 ff ff 73 01 c3 e8 e8 80 03 00 81 c1 f6 5f 09 00
>> [  245.703680] EAX: ffffffda EBX: affa4efa ECX: affa4f03 EDX: 080d3630
>> [  245.704642] ESI: 00008010 EDI: 00000000 EBP: 00000000 ESP: affa45c0
>> [  245.705637] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b EFLAGS: 00000282
> 
> There is not a q->queue_lock as blk-legacy to serialize floppy_queue_rq from different contexts.

Doesn't look immediately racy, the internal queue list is protected by
the floppy_lock, and the busy start is marked by atomic bit setting.
Do you see an issue with it, or are you just pontificating?

FWIW, just ran qemu with two floppy drives and concurrent access,
didn't see an issue.

-- 
Jens Axboe