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SubjectWARNING: bad unlock balance in __get_user_pages_remote
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Hello,

syzbot found the following crash on:

HEAD commit: 7e634208 Merge tag 'acpi-5.7-rc1-2' of git://git.kernel.or..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=169498ede00000
kernel config: https://syzkaller.appspot.com/x/.config?x=12205d036cec317f
dashboard link: https://syzkaller.appspot.com/bug?extid=a8c70b7f3579fc0587dc
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17a41543e00000

The bug was bisected to:

commit 71335f37c5e8ec9225285206f7f875057b9737ad
Author: Peter Xu <peterx@redhat.com>
Date: Thu Apr 2 04:08:53 2020 +0000

mm/gup: allow to react to fatal signals

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=17dba9b3e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=143ba9b3e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=103ba9b3e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a8c70b7f3579fc0587dc@syzkaller.appspotmail.com
Fixes: 71335f37c5e8 ("mm/gup: allow to react to fatal signals")

=====================================
WARNING: bad unlock balance detected!
5.6.0-syzkaller #0 Not tainted
-------------------------------------
syz-executor.0/8429 is trying to release lock (&mm->mmap_sem) at:
[<ffffffff819fbf60>] __get_user_pages_locked mm/gup.c:1366 [inline]
[<ffffffff819fbf60>] __get_user_pages_remote mm/gup.c:1831 [inline]
[<ffffffff819fbf60>] __get_user_pages_remote+0x540/0x740 mm/gup.c:1806
but there are no more locks to release!

other info that might help us debug this:
no locks held by syz-executor.0/8429.

stack backtrace:
CPU: 0 PID: 8429 Comm: syz-executor.0 Not tainted 5.6.0-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+0x188/0x20d lib/dump_stack.c:118
__lock_release kernel/locking/lockdep.c:4633 [inline]
lock_release+0x586/0x800 kernel/locking/lockdep.c:4941
up_read+0x79/0x750 kernel/locking/rwsem.c:1573
__get_user_pages_locked mm/gup.c:1366 [inline]
__get_user_pages_remote mm/gup.c:1831 [inline]
__get_user_pages_remote+0x540/0x740 mm/gup.c:1806
pin_user_pages_remote+0x67/0xa0 mm/gup.c:2897
process_vm_rw_single_vec mm/process_vm_access.c:108 [inline]
process_vm_rw_core.isra.0+0x423/0x940 mm/process_vm_access.c:218
process_vm_rw+0x21f/0x240 mm/process_vm_access.c:286
__do_sys_process_vm_writev mm/process_vm_access.c:308 [inline]
__se_sys_process_vm_writev mm/process_vm_access.c:303 [inline]
__x64_sys_process_vm_writev+0xdf/0x1b0 mm/process_vm_access.c:303
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45c879
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fa1008bac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000137
RAX: ffffffffffffffda RBX: 00007fa1008bb6d4 RCX: 000000000045c879
RDX: 0000000000000001 RSI: 0000000020c22000 RDI: 0000000000000009
RBP: 000000000076bf00 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000020c22fa0 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000085d R14: 00000000004cb1ee R15: 000000000076bf0c
------------[ cut here ]------------
DEBUG_RWSEMS_WARN_ON(tmp < 0): count = 0xffffffffffffff00, magic = 0xffff888094028338, owner = 0x3, curr 0xffff888093cbc500, list empty
WARNING: CPU: 0 PID: 8429 at kernel/locking/rwsem.c:1435 __up_read kernel/locking/rwsem.c:1435 [inline]
WARNING: CPU: 0 PID: 8429 at kernel/locking/rwsem.c:1435 up_read+0x5f9/0x750 kernel/locking/rwsem.c:1574


---
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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