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SubjectINFO: task hung in __generic_file_fsync (2)
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Hello,

syzbot found the following crash on:

HEAD commit: bf8d1cd4 Merge tag 'scsi-fixes' of git://git.kernel.org/pu..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11b80869e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35
dashboard link: https://syzkaller.appspot.com/bug?extid=44c32606d8669fb0d45c
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=137e2615e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11306971e00000

The bug was bisected to:

commit 6dc4f100c175dd0511ae8674786e7c9006cdfbfa
Author: Ming Lei <ming.lei@redhat.com>
Date: Fri Feb 15 11:13:19 2019 +0000

block: allow bio_for_each_segment_all() to iterate over multi-page bvec

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=130c5e49e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=108c5e49e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=170c5e49e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+44c32606d8669fb0d45c@syzkaller.appspotmail.com
Fixes: 6dc4f100c175 ("block: allow bio_for_each_segment_all() to iterate
over multi-page bvec")

INFO: task syz-executor072:10629 blocked for more than 143 seconds.
Not tainted 5.5.0-rc3-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor072 D25264 10629 10066 0x00004004
Call Trace:
context_switch kernel/sched/core.c:3385 [inline]
__schedule+0x934/0x1f90 kernel/sched/core.c:4081
schedule+0xdc/0x2b0 kernel/sched/core.c:4155
io_schedule+0x1c/0x70 kernel/sched/core.c:5799
wait_on_page_bit_common mm/filemap.c:1175 [inline]
wait_on_page_bit+0x27c/0xa60 mm/filemap.c:1224
wait_on_page_writeback+0x1b2/0x4f0 mm/page-writeback.c:2822
__filemap_fdatawait_range+0x145/0x340 mm/filemap.c:526
file_write_and_wait_range+0x1ac/0x210 mm/filemap.c:786
__generic_file_fsync+0x79/0x200 fs/libfs.c:1000
fat_file_fsync+0x78/0x210 fs/fat/file.c:190
vfs_fsync_range+0x141/0x230 fs/sync.c:197
generic_write_sync include/linux/fs.h:2856 [inline]
generic_file_write_iter+0x4ea/0x68e mm/filemap.c:3474
call_write_iter include/linux/fs.h:1902 [inline]
do_iter_readv_writev+0x5f8/0x8f0 fs/read_write.c:693
do_iter_write fs/read_write.c:970 [inline]
do_iter_write+0x184/0x610 fs/read_write.c:951
vfs_iter_write+0x77/0xb0 fs/read_write.c:983
iter_file_splice_write+0x717/0xc10 fs/splice.c:760
do_splice_from fs/splice.c:863 [inline]
direct_splice_actor+0x123/0x190 fs/splice.c:1037
splice_direct_to_actor+0x3b4/0xa30 fs/splice.c:992
do_splice_direct+0x1da/0x2a0 fs/splice.c:1080
do_sendfile+0x597/0xd00 fs/read_write.c:1464
__do_sys_sendfile64 fs/read_write.c:1525 [inline]
__se_sys_sendfile64 fs/read_write.c:1511 [inline]
__x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1511
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x445e59
Code: Bad RIP value.
RSP: 002b:00007ffc4bfab018 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000445e59
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000402fe0 R09: 0000000000402fe0
R10: 00008080fffffffe R11: 0000000000000246 R12: 0000000000000082
R13: 0000000000402fe0 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1116:
#0: ffffffff899a5680 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x279 kernel/locking/lockdep.c:5334
1 lock held by rs:main Q:Reg/9913:
#0: ffff8880ae937358 (&rq->lock){-.-.}, at: newidle_balance+0xa28/0xe80
kernel/sched/fair.c:10177
1 lock held by rsyslogd/9915:
#0: ffff888087f713e0 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:801
2 locks held by getty/10037:
#0: ffff8880a2d26090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018132e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/10038:
#0: ffff88809f419090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018932e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/10039:
#0: ffff8880a2725090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018732e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/10040:
#0: ffff8880966a2090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018832e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/10041:
#0: ffff88809e168090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900017f32e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/10042:
#0: ffff8880a7c45090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900018332e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/10043:
#0: ffff88809958e090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900011402e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
1 lock held by syz-executor072/10629:
#0: ffff88809a52a428 (sb_writers#9){.+.+}, at: file_start_write
include/linux/fs.h:2885 [inline]
#0: ffff88809a52a428 (sb_writers#9){.+.+}, at: do_sendfile+0x9b9/0xd00
fs/read_write.c:1463

=============================================

NMI backtrace for cpu 0
CPU: 0 PID: 1116 Comm: khungtaskd Not tainted 5.5.0-rc3-syzkaller #0
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+0x197/0x210 lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x23b/0x28b 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:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xb11/0x10c0 kernel/hung_task.c:289
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0xe/0x10
arch/x86/include/asm/irqflags.h:60


---
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@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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