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Date
SubjectINFO: task hung in fb_compat_ioctl
From
Hello,

syzbot found the following crash on:

HEAD commit: 687dec9b Merge tag 'erofs-for-5.5-rc2-fixes' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16979cfae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=061df5e46ec99b40552c
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386

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+061df5e46ec99b40552c@syzkaller.appspotmail.com

INFO: task syz-executor.2:25386 blocked for more than 143 seconds.
Not tainted 5.5.0-rc1-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.2 D29712 25386 9095 0x20020004
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
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:4214
__mutex_lock_common kernel/locking/mutex.c:1036 [inline]
__mutex_lock+0x7ab/0x13c0 kernel/locking/mutex.c:1106
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1121
lock_fb_info include/linux/fb.h:637 [inline]
fb_get_fscreeninfo drivers/video/fbdev/core/fbmem.c:1283 [inline]
fb_compat_ioctl+0x6ed/0xc50 drivers/video/fbdev/core/fbmem.c:1314
__do_compat_sys_ioctl fs/compat_ioctl.c:214 [inline]
__se_compat_sys_ioctl fs/compat_ioctl.c:142 [inline]
__ia32_compat_sys_ioctl+0x233/0x610 fs/compat_ioctl.c:142
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f41a39
Code: Bad RIP value.
RSP: 002b:00000000f5d1c0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000004602
RDX: 0000000020000080 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
INFO: task syz-executor.2:25392 blocked for more than 143 seconds.
Not tainted 5.5.0-rc1-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.2 D28520 25392 9095 0x20020004
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
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:4214
__mutex_lock_common kernel/locking/mutex.c:1036 [inline]
__mutex_lock+0x7ab/0x13c0 kernel/locking/mutex.c:1106
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1121
lock_fb_info include/linux/fb.h:637 [inline]
fb_open+0xd7/0x450 drivers/video/fbdev/core/fbmem.c:1406
chrdev_open+0x245/0x6b0 fs/char_dev.c:414
do_dentry_open+0x4e6/0x1380 fs/open.c:797
vfs_open+0xa0/0xd0 fs/open.c:914
do_last fs/namei.c:3420 [inline]
path_openat+0x10df/0x4500 fs/namei.c:3537
do_filp_open+0x1a1/0x280 fs/namei.c:3567
do_sys_open+0x3fe/0x5d0 fs/open.c:1097
__do_compat_sys_openat fs/open.c:1143 [inline]
__se_compat_sys_openat fs/open.c:1141 [inline]
__ia32_compat_sys_openat+0x98/0xf0 fs/open.c:1141
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f41a39
Code: Bad RIP value.
RSP: 002b:00000000f5cda0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00000000ffffff9c RCX: 0000000020000180
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
1 lock held by khungtaskd/1113:
#0: ffffffff899a56c0 (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x279 kernel/locking/lockdep.c:5334
1 lock held by rsyslogd/8960:
#0: ffff88808c2640e0 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:801
2 locks held by getty/9050:
#0: ffff88809b3bf090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900017cb2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9051:
#0: ffff888095020090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc9000184b2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9052:
#0: ffff8880a322a090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc9000182b2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9053:
#0: ffff88809a312090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc9000183b2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9054:
#0: ffff8880935fc090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc900017eb2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9055:
#0: ffff88809edd6090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc9000181b2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by getty/9056:
#0: ffff8880959b2090 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:340
#1: ffffc9000178b2e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x220/0x1bf0 drivers/tty/n_tty.c:2156
2 locks held by syz-executor.2/25382:
1 lock held by syz-executor.2/25386:
#0: ffff888218cbf070 (&fb_info->lock){+.+.}, at: lock_fb_info
include/linux/fb.h:637 [inline]
#0: ffff888218cbf070 (&fb_info->lock){+.+.}, at: fb_get_fscreeninfo
drivers/video/fbdev/core/fbmem.c:1283 [inline]
#0: ffff888218cbf070 (&fb_info->lock){+.+.}, at:
fb_compat_ioctl+0x6ed/0xc50 drivers/video/fbdev/core/fbmem.c:1314
1 lock held by syz-executor.2/25392:
#0: ffff888218cbf070 (&fb_info->lock){+.+.}, at: lock_fb_info
include/linux/fb.h:637 [inline]
#0: ffff888218cbf070 (&fb_info->lock){+.+.}, at: fb_open+0xd7/0x450
drivers/video/fbdev/core/fbmem.c:1406

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

NMI backtrace for cpu 0
CPU: 0 PID: 1113 Comm: khungtaskd Not tainted 5.5.0-rc1-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
CPU: 1 PID: 25382 Comm: syz-executor.2 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:__writeq arch/x86/include/asm/io.h:98 [inline]
RIP: 0010:bitfill_aligned drivers/video/fbdev/core/cfbfillrect.c:50 [inline]
RIP: 0010:bitfill_aligned+0xaa/0x210
drivers/video/fbdev/core/cfbfillrect.c:35
Code: 31 ff 4c 89 fe e8 46 9b c0 fd 4d 85 ff 74 09 e8 9c 99 c0 fd 4c 21 7d
d0 e8 93 99 c0 fd 49 8b 06 48 31 c3 48 23 5d d0 48 31 c3 <49> 89 1e e8 7e
99 c0 fd 48 83 c4 18 5b 41 5c 41 5d 41 5e 41 5f 5d
RSP: 0018:ffffc90001567388 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffc9000daef000
RDX: 0000000000040000 RSI: ffffffff83b491fd RDI: 0000000000000007
RBP: ffffc900015673c8 R08: ffff88808cdf4100 R09: 0000000000000040
R10: ffffed10147ab25b R11: ffff8880a3d592df R12: 0000000000000040
R13: 0000000000000040 R14: ffff8880000a0000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8880ae900000(0063) knlGS:00000000f5d3db40
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00007f793125b140 CR3: 00000000a520a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
cfb_fillrect+0x423/0x7c0 drivers/video/fbdev/core/cfbfillrect.c:327
vga16fb_fillrect+0x6ce/0x19b0 drivers/video/fbdev/vga16fb.c:951
bit_clear_margins+0x30b/0x530 drivers/video/fbdev/core/bitblit.c:232
fbcon_clear_margins+0x1e9/0x250 drivers/video/fbdev/core/fbcon.c:1372
fbcon_switch+0xd7f/0x17f0 drivers/video/fbdev/core/fbcon.c:2354
redraw_screen+0x2b6/0x7d0 drivers/tty/vt/vt.c:997
fbcon_modechanged+0x5c3/0x790 drivers/video/fbdev/core/fbcon.c:2991
fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
do_fb_ioctl+0x390/0x7d0 drivers/video/fbdev/core/fbmem.c:1104
fb_compat_ioctl+0x305/0xc50 drivers/video/fbdev/core/fbmem.c:1310
__do_compat_sys_ioctl fs/compat_ioctl.c:214 [inline]
__se_compat_sys_ioctl fs/compat_ioctl.c:142 [inline]
__ia32_compat_sys_ioctl+0x233/0x610 fs/compat_ioctl.c:142
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x27b/0xe16 arch/x86/entry/common.c:408
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f41a39
Code: 00 00 00 89 d3 5b 5e 5f 5d c3 b8 80 96 98 00 eb c4 8b 04 24 c3 8b 1c
24 c3 8b 34 24 c3 8b 3c 24 c3 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f5d3d0cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000004601
RDX: 0000000020000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000


---
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.

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