Date:   Mon, 30 Apr 2018 19:55:03 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+221d75710bde87fa0e97@...kaller.appspotmail.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: INFO: task hung in lock_mount

On Mon, Apr 30, 2018 at 7:46 PM, syzbot
<syzbot+221d75710bde87fa0e97@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    a27fc14219f2 Merge branch 'parisc-4.17-3' of
> git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?id=5953322812964864
> kernel config:
> https://syzkaller.appspot.com/x/.config?id=-5914490758943236750
> dashboard link: https://syzkaller.appspot.com/bug?extid=221d75710bde87fa0e97
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+221d75710bde87fa0e97@...kaller.appspotmail.com


It seems this thread is in infinite loop printing:

[  643.736460] b_state=0x00000029, b_size=512
[  643.740722] device loop0 blocksize: 4096
[  643.744857] __find_get_block_slow() failed. block=1, b_blocknr=8
[  643.751020] b_state=0x00000029, b_size=512
[  643.755271] device loop0 blocksize: 4096
[  643.759349] __find_get_block_slow() failed. block=1, b_blocknr=8
[  643.765540] b_state=0x00000029, b_size=512
...



> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> INFO: task syz-executor0:20276 blocked for more than 120 seconds.
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
>       Not tainted 4.17.0-rc1+ #6
> b_state=0x00000029, b_size=512
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor0   D24704 20276  23010 0x00000004
> device loop0 blocksize: 4096
> Call Trace:
>  context_switch kernel/sched/core.c:2848 [inline]
>  __schedule+0x801/0x1e30 kernel/sched/core.c:3490
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  schedule+0xef/0x430 kernel/sched/core.c:3549
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  __rwsem_down_write_failed_common+0x919/0x15d0
> kernel/locking/rwsem-xadd.c:566
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
>  rwsem_down_write_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:595
> device loop0 blocksize: 4096
>  call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  __down_write arch/x86/include/asm/rwsem.h:142 [inline]
>  down_write+0xa2/0x120 kernel/locking/rwsem.c:72
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
>  inode_lock include/linux/fs.h:713 [inline]
>  lock_mount+0x8c/0x2e0 fs/namespace.c:2087
> device loop0 blocksize: 4096
>  do_add_mount+0x27/0x370 fs/namespace.c:2464
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  do_new_mount fs/namespace.c:2531 [inline]
>  do_mount+0x18e6/0x3070 fs/namespace.c:2847
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  ksys_mount+0x12d/0x140 fs/namespace.c:3063
>  __do_sys_mount fs/namespace.c:3077 [inline]
>  __se_sys_mount fs/namespace.c:3074 [inline]
>  __x64_sys_mount+0xbe/0x150 fs/namespace.c:3074
> b_state=0x00000029, b_size=512
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
> b_state=0x00000029, b_size=512
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x455329
> device loop0 blocksize: 4096
> RSP: 002b:00007f68cf133c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007f68cf1346d4 RCX: 0000000000455329
> __find_get_block_slow() failed. block=1, b_blocknr=8
> RDX: 0000000020000240 RSI: 0000000020000080 RDI: 0000000020000280
> RBP: 000000000072bf58 R08: 0000000020000040 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> b_state=0x00000029, b_size=512
> R13: 00000000000003fb R14: 00000000006f9028 R15: 0000000000000001
>
> Showing all locks held in the system:
> device loop0 blocksize: 4096
> 2 locks held by khungtaskd/888:
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  #0: 00000000a9a44477 (
> b_state=0x00000029, b_size=512
> rcu_read_lock){....}, at: check_hung_uninterruptible_tasks
> kernel/hung_task.c:175 [inline]
> rcu_read_lock){....}, at: watchdog+0x1ff/0xf60 kernel/hung_task.c:249
> device loop0 blocksize: 4096
>  #1: 000000009ff2053f (tasklist_lock){.+.+}, at:
> debug_show_all_locks+0xde/0x34a kernel/locking/lockdep.c:4470
> 2 locks held by getty/4439:
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  #0: 00000000c9b76b9a (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  #1:
> b_state=0x00000029, b_size=512
> 000000000e5cb710 (&ldata->atomic_read_lock){+.+.}
> device loop0 blocksize: 4096
> , at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4440:
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  #0: 000000005b768cd3 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
>  #1: 00000000addaef00 (
> __find_get_block_slow() failed. block=1, b_blocknr=8
> &ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0
> drivers/tty/n_tty.c:2131
> 2 locks held by getty/4441:
>  #0: 000000000c8a520e (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 00000000be9918f7 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4442:
>  #0: 0000000029e321e8 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 00000000c3a0104f (&ldata->atomic_read_lock
> b_state=0x00000029, b_size=512
> ){+.+.}, at: n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4443:
> device loop0 blocksize: 4096
>  #0: 00000000b12d6ffd (
> __find_get_block_slow() failed. block=1, b_blocknr=8
> &tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1:
> b_state=0x00000029, b_size=512
> 00000000625407e7 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4444:
> device loop0 blocksize: 4096
>  #0: 0000000019948f4c (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1:
> __find_get_block_slow() failed. block=1, b_blocknr=8
> 00000000071c1ff8 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x321/0x1cc0 drivers/tty/n_tty.c:2131
> 2 locks held by getty/4445:
> b_state=0x00000029, b_size=512
>  #0: 00000000fe9e0006 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
> device loop0 blocksize: 4096
>  #1: 00000000a738c9c9 (
> __find_get_block_slow() failed. block=1, b_blocknr=8
> &ldata->atomic_read_lock){+.+.}, at: n_tty_read+0x321/0x1cc0
> drivers/tty/n_tty.c:2131
> 1 lock held by syz-executor0/20276:
> b_state=0x00000029, b_size=512
>  #0: 00000000a1afb949 (&sb->s_type->i_mutex_key#16){++++}
> device loop0 blocksize: 4096
> , at: inode_lock include/linux/fs.h:713 [inline]
> , at: lock_mount+0x8c/0x2e0 fs/namespace.c:2087
> 2 locks held by syz-executor0/20277:
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  #0: 000000008134fa51 (sb_writers#14){.+.+}, at: sb_start_write
> include/linux/fs.h:1550 [inline]
>  #0: 000000008134fa51 (sb_writers#14){.+.+}, at: mnt_want_write+0x3f/0xc0
> fs/namespace.c:386
>  #1: 00000000a1afb949
> b_state=0x00000029, b_size=512
> device loop0 blocksize: 4096
>  (&sb->s_type->i_mutex_key#16/1
> __find_get_block_slow() failed. block=1, b_blocknr=8
> ){+.+.}, at: inode_lock_nested include/linux/fs.h:748 [inline]
> ){+.+.}, at: filename_create+0x1aa/0x5a0 fs/namei.c:3606
> 1 lock held by syz-executor0/20279:
>  #0:
> b_state=0x00000029, b_size=512
> 00000000a1afb949 (&sb->s_type->i_mutex_key#16){++++}, at: inode_lock
> include/linux/fs.h:713 [inline]
> 00000000a1afb949 (&sb->s_type->i_mutex_key#16){++++}, at:
> lock_mount+0x8c/0x2e0 fs/namespace.c:2087
>
> device loop0 blocksize: 4096
> =============================================
>
> NMI backtrace for cpu 0
> CPU: 0 PID: 888 Comm: khungtaskd Not tainted 4.17.0-rc1+ #6
> __find_get_block_slow() failed. block=1, b_blocknr=8
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>  nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
> b_state=0x00000029, b_size=512
>  nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
>  arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
>  trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
>  check_hung_task kernel/hung_task.c:132 [inline]
>  check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
>  watchdog+0xc10/0xf60 kernel/hung_task.c:249
> device loop0 blocksize: 4096
> __find_get_block_slow() failed. block=1, b_blocknr=8
>  kthread+0x345/0x410 kernel/kthread.c:238
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
> Sending NMI from CPU 0 to CPUs 1:
> b_state=0x00000029, b_size=512
> NMI backtrace for cpu 1
> CPU: 1 PID: 20216 Comm: syz-executor0 Not tainted 4.17.0-rc1+ #6
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x1/0x20 kernel/kcov.c:187
> RSP: 0018:ffff8801db107d88 EFLAGS: 00000006
> RAX: ffff8801d11bc6c0 RBX: ffff8801db11f0c0 RCX: ffffffff816b3515
> RDX: 0000000000010000 RSI: 0000000000000003 RDI: 0000000000000003
> RBP: ffff8801db107dc0 R08: ffff8801d11bc6c0 R09: ffffed003b624b80
> R10: ffffed003b624b80 R11: ffff8801db125c03 R12: 000000ac0c601b80
> R13: 0000000000000000 R14: 0000000000000003 R15: ffff8801db125c00
> FS:  00007f68cf155700(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffffff600400 CR3: 00000001d8a72000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <IRQ>
>  tick_program_event+0xab/0x130 kernel/time/tick-oneshot.c:48
>  hrtimer_interrupt+0x2db/0x650 kernel/time/hrtimer.c:1519
>  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
>  smp_apic_timer_interrupt+0x15d/0x710 arch/x86/kernel/apic/apic.c:1050
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
>  </IRQ>
> RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783
> [inline]
> RIP: 0010:console_trylock_spinning kernel/printk/printk.c:1678 [inline]
> RIP: 0010:vprintk_emit+0xbd0/0xdd0 kernel/printk/printk.c:1906
> RSP: 0018:ffff88018a2df000 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
> RAX: 0000000000040000 RBX: 0000000000000200 RCX: ffffc90003ac6000
> RDX: 0000000000040000 RSI: ffffffff8160bbb7 RDI: 0000000000000246
> RBP: ffff88018a2df190 R08: ffff8801d11bcef8 R09: 0000000000000006
> R10: ffff8801d11bc6c0 R11: 0000000000000000 R12: 1ffffffff116312d
> R13: 000000000000001e R14: ffffed003145be1d R15: ffffffff8a49a360
>  vprintk_default+0x28/0x30 kernel/printk/printk.c:1947
>  vprintk_func+0x7a/0xe7 kernel/printk/printk_safe.c:379
>  printk+0x9e/0xba kernel/printk/printk.c:1980
>  __find_get_block_slow fs/buffer.c:235 [inline]
>  __find_get_block.cold.58+0x85/0x103 fs/buffer.c:1287
>  __getblk_slow fs/buffer.c:1032 [inline]
>  __getblk_gfp+0x2a1/0xaf0 fs/buffer.c:1313
>  __bread_gfp+0x2d/0x310 fs/buffer.c:1347
>  sb_bread include/linux/buffer_head.h:309 [inline]
>  fat__get_entry+0x594/0xa20 fs/fat/dir.c:101
>  fat_get_entry fs/fat/dir.c:129 [inline]
>  fat_search_long+0x33b/0x15d0 fs/fat/dir.c:477
>  vfat_find+0x16d/0x1a0 fs/fat/namei_vfat.c:697
>  vfat_lookup+0xfc/0x6d0 fs/fat/namei_vfat.c:720
>  __lookup_hash+0x12e/0x190 fs/namei.c:1505
>  filename_create+0x1dd/0x5a0 fs/namei.c:3607
>  user_path_create fs/namei.c:3664 [inline]
>  do_mkdirat+0xd2/0x2f0 fs/namei.c:3802
>  __do_sys_mkdir fs/namei.c:3826 [inline]
>  __se_sys_mkdir fs/namei.c:3824 [inline]
>  __x64_sys_mkdir+0x5c/0x80 fs/namei.c:3824
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x455329
> RSP: 002b:00007f68cf154c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
> RAX: ffffffffffffffda RBX: 00007f68cf1556d4 RCX: 0000000000455329
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000080
> RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000000003eb R14: 00000000006f8ea8 R15: 0000000000000000
> Code: a6 fe ff ff 5d c3 0f 1f 40 00 55 0f b7 d6 0f b7 f7 bf 03 00 00 00 48
> 89 e5 48 8b 4d 08 e8 88 fe ff ff 5d c3 66 0f 1f 44 00 00 55 <89> f2 89 fe bf
> 05 00 00 00 48 89 e5 48 8b 4d 08 e8 6a fe ff ff
> INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 1.012
> msecs
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report.
> If you forgot to add the Reported-by tag, once the fix for this bug is
> merged
> into any tree, please reply to this email with:
> #syz fix: exact-commit-title
> To mark this as a duplicate of another syzbot report, please reply with:
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> If it's a one-off invalid bug report, please reply with:
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