Message-ID: <CACT4Y+YJmoeBtdg6KB38pOHWiuFLGxgbkD5v4Oex2rbuxN=YWQ@mail.gmail.com>
Date:   Mon, 9 Jul 2018 19:08:12 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+9d0373cdac2be4979750@...kaller.appspotmail.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        David Miller <davem@...emloft.net>,
        v9fs-developer@...ts.sourceforge.net,
        netdev <netdev@...r.kernel.org>
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 vfs_removexattr

On Mon, Jul 9, 2018 at 7:07 PM, syzbot
<syzbot+9d0373cdac2be4979750@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    1e4b044d2251 Linux 4.18-rc4
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14dc81b2400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
> dashboard link: https://syzkaller.appspot.com/bug?extid=9d0373cdac2be4979750
> 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+9d0373cdac2be4979750@...kaller.appspotmail.com

This looks suspiciously similar to "INFO: task hung in vfs_setxattr":
https://syzkaller.appspot.com/bug?id=719b006d5ff2c98e95b3db1d442771de9fcbfb93

Also caused by 9p program:

14:02:00 executing program 5:
pipe2$9p(&(0x7f0000000100)={<r0=>0xffffffffffffffff,
<r1=>0xffffffffffffffff}, 0x0)
write$P9_RUNLINKAT(r1, &(0x7f0000000040)={0xffffffffffffffca, 0x4d}, 0x7)
mkdir(&(0x7f0000000140)='./file0\x00', 0x0)
mount$9p_fd(0x0, &(0x7f00000000c0)='./file0\x00',
&(0x7f0000000340)='9p\x00', 0x0, &(0x7f00000001c0)={'trans=fd,',
{'rfdno', 0x3d, r0}, 0x2c, {'wfdno', 0x3d, r1}, 0x2c})
write$P9_RREADDIR(r1, &(0x7f0000000480)={0x2a, 0x29, 0x1, {0x0, [{{},
0x0, 0x0, 0x7, './file0'}]}}, 0x2a)
write$P9_RGETATTR(r1, &(0x7f0000000200)={0xa0, 0x19, 0x1}, 0xa0)
write$P9_RREADDIR(r1, &(0x7f00000004c0)={0x313, 0x29, 0x1, {0x0,
[{{0x2, 0x3, 0x7}, 0x10001, 0x3, 0x7, './file0'}, {{0x1d, 0x4, 0x5},
0x100000000, 0x8, 0x7, './file1'}, {{0x4, 0x2, 0x4}, 0x3, 0x6, 0x7,
'./file0'}, {{0x120, 0x2, 0x2}, 0x979, 0x4, 0x7, './file0'},
{{0x4f5f4daf2e09cfcf, 0x4, 0x6}, 0x1000, 0x1, 0x7, './file0'}, {{0x82,
0x1, 0x2}, 0x5, 0x2, 0x7, './file0'}, {{0x40, 0x1, 0x7}, 0x2, 0x6,
0x7, './file0'}, {{0x40, 0x1, 0x2}, 0x7fffffff, 0x983d, 0x7,
'./file0'}, {{0x40, 0x3, 0x4}, 0x2, 0x5, 0x7, './file0'}, {{0x60, 0x1,
0x3}, 0x7ff, 0x7, 0x7, './file0'}]}}, 0x141)
r2 = openat$pfkey(0xffffffffffffff9c,
&(0x7f0000000300)='/proc/self/net/pfkey\x00', 0x1, 0x0)
bind(r2, &(0x7f0000000780)=@...ernet={0x306, @broadcast=[0xff, 0xff,
0xff, 0xff, 0xff, 0xff]}, 0x80)
write$P9_RWSTAT(r1, &(0x7f00000002c0)={0x7, 0x7f, 0x1}, 0x7)
mount$9p_fd(0x0, &(0x7f0000000000)='./file0\x00',
&(0x7f0000000900)='9p\x00', 0x0, &(0x7f0000000840)={'trans=fd,',
{'rfdno', 0x3d, r0}, 0x2c, {'wfdno', 0x3d, r1}, 0x2c,
{[{@...ess_uid={'access', 0x3d}, 0x2c}]}})
removexattr(&(0x7f0000000380)='./file0\x00',
&(0x7f0000000400)=@...wn='system.posix_acl_default\x00')
r3 = syz_open_dev$midi(&(0x7f0000000080)='/dev/midi#\x00', 0x1ff, 0x400)
r4 = fcntl$getown(r1, 0x9)
accept4$alg(r2, 0x0, 0x0, 0x0)
ioctl$SNDRV_CTL_IOCTL_ELEM_INFO(r3, 0xc1105511,
&(0x7f0000000640)={{0x4, 0x1, 0x81, 0x5b94, '\x00', 0x3b2}, 0x2, 0x1,
0x90, r4, 0x3, 0x8, 'syz0\x00', &(0x7f0000000180)=['\x00', '+@,\x00',
')\x00'], 0x7, [], [0x6, 0x10000, 0x2, 0x8]})


> netlink: 16 bytes leftover after parsing attributes in process
> `syz-executor0'.
> netlink: 16 bytes leftover after parsing attributes in process
> `syz-executor0'.
> INFO: task syz-executor5:14548 blocked for more than 140 seconds.
>       Not tainted 4.18.0-rc4+ #138
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> syz-executor5   D24752 14548   4547 0x00000004
> Call Trace:
>  context_switch kernel/sched/core.c:2853 [inline]
>  __schedule+0x87c/0x1ed0 kernel/sched/core.c:3501
>  schedule+0xfb/0x450 kernel/sched/core.c:3545
>  __rwsem_down_write_failed_common+0x95d/0x1630
> kernel/locking/rwsem-xadd.c:566
>  rwsem_down_write_failed+0xe/0x10 kernel/locking/rwsem-xadd.c:595
>  call_rwsem_down_write_failed+0x17/0x30 arch/x86/lib/rwsem.S:117
>  __down_write arch/x86/include/asm/rwsem.h:142 [inline]
>  down_write+0xaa/0x130 kernel/locking/rwsem.c:72
>  inode_lock include/linux/fs.h:715 [inline]
>  vfs_removexattr+0x82/0x1c0 fs/xattr.c:391
>  removexattr+0xd3/0x130 fs/xattr.c:691
>  path_removexattr+0x1b9/0x210 fs/xattr.c:705
>  __do_sys_removexattr fs/xattr.c:719 [inline]
>  __se_sys_removexattr fs/xattr.c:716 [inline]
>  __x64_sys_removexattr+0x59/0x80 fs/xattr.c:716
>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x455e29
> Code: cc 64 48 8b 0c 25 f8 ff ff ff 48 3b 61 10 0f 86 ab 04 00 00 48 83 ec
> 58 48 89 6c 24 50 48 8d 6c 24 50 48 8b 44 24 60 c6 00 00 <48> 8b 4c 24 68 48
> 89 ca 48 89 50 08 48 8b 59 20 48 01 da 31 db 31
> RSP: 002b:00007f4465180c68 EFLAGS: 00000246 ORIG_RAX: 00000000000000c5
> RAX: ffffffffffffffda RBX: 00007f44651816d4 RCX: 0000000000455e29
> RDX: 0000000000000000 RSI: 0000000020000400 RDI: 0000000020000380
> RBP: 000000000072bf48 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> R13: 00000000004bbfeb R14: 00000000004d1108 R15: 0000000000000001
>
> Showing all locks held in the system:
> 1 lock held by khungtaskd/901:
>  #0: 00000000ebf24c36 (rcu_read_lock){....}, at:
> debug_show_all_locks+0xd0/0x428 kernel/locking/lockdep.c:4461
> 1 lock held by rsyslogd/4405:
> 2 locks held by getty/4495:
>  #0: 00000000692a9d2f (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 0000000072fe5412 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4496:
>  #0: 000000002b623882 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 0000000056c15f7c (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4497:
>  #0: 000000002c1f858b (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 0000000048aba06b (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4498:
>  #0: 00000000da02f89a (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 000000004a06c40f (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4499:
>  #0: 0000000017508207 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 00000000a4b24877 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4500:
>  #0: 0000000079a247d3 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 000000009bcfd45d (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by getty/4501:
>  #0: 00000000e73958a9 (&tty->ldisc_sem){++++}, at: ldsem_down_read+0x37/0x40
> drivers/tty/tty_ldsem.c:365
>  #1: 000000007d96a629 (&ldata->atomic_read_lock){+.+.}, at:
> n_tty_read+0x335/0x1ce0 drivers/tty/n_tty.c:2140
> 2 locks held by syz-executor5/14500:
>  #0: 00000000ba1ef7f9 (sb_writers#19){.+.+}, at: sb_start_write
> include/linux/fs.h:1554 [inline]
>  #0: 00000000ba1ef7f9 (sb_writers#19){.+.+}, at: mnt_want_write+0x3f/0xc0
> fs/namespace.c:386
>  #1: 00000000e4cbde96 (&sb->s_type->i_mutex_key#25){++++}, at: inode_lock
> include/linux/fs.h:715 [inline]
>  #1: 00000000e4cbde96 (&sb->s_type->i_mutex_key#25){++++}, at:
> vfs_removexattr+0x82/0x1c0 fs/xattr.c:391
> 2 locks held by syz-executor5/14548:
>  #0: 00000000ba1ef7f9 (sb_writers#19){.+.+}, at: sb_start_write
> include/linux/fs.h:1554 [inline]
>  #0: 00000000ba1ef7f9 (sb_writers#19){.+.+}, at: mnt_want_write+0x3f/0xc0
> fs/namespace.c:386
>  #1: 00000000e4cbde96 (&sb->s_type->i_mutex_key#25){++++}, at: inode_lock
> include/linux/fs.h:715 [inline]
>  #1: 00000000e4cbde96 (&sb->s_type->i_mutex_key#25){++++}, at:
> vfs_removexattr+0x82/0x1c0 fs/xattr.c:391
>
> =============================================
>
> NMI backtrace for cpu 0
> CPU: 0 PID: 901 Comm: khungtaskd Not tainted 4.18.0-rc4+ #138
> 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+0x1c9/0x2b4 lib/dump_stack.c:113
>  nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
>  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_uninterruptible_tasks kernel/hung_task.c:196 [inline]
>  watchdog+0x9c4/0xf80 kernel/hung_task.c:252
>  kthread+0x345/0x410 kernel/kthread.c:246
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
> Sending NMI from CPU 0 to CPUs 1:
> NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10
> arch/x86/include/asm/irqflags.h:54
>
>
> ---
> 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. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
>
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