WARNING: lock held when returning to user space in lo_ioctl

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 65640c873dcf Linux 4.14.292
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1621ed07080000
kernel config: https://syzkaller.appspot.com/x/.config?x=e88a9c332b8ce547
dashboard link: https://syzkaller.appspot.com/bug?extid=c1d8ca717a93d3a2e7b4
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c1d8ca...@syzkaller.appspotmail.com

================================================
WARNING: lock held when returning to user space!
4.14.292-syzkaller #0 Not tainted
------------------------------------------------
syz-executor.1/22542 is leaving the kernel with locks still held!
1 lock held by syz-executor.1/22542:
#0: (&lo->lo_ctl_mutex/1){+.+.}, at: [<ffffffff838d8187>] lo_ioctl+0x87/0x1cd0 drivers/block/loop.c:1419


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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 5df8b4735177 Linux 4.14.293
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=121ab428880000
kernel config: https://syzkaller.appspot.com/x/.config?x=cc7e9ed39471e56f

dashboard link: https://syzkaller.appspot.com/bug?extid=c1d8ca717a93d3a2e7b4
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=166e1428880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=170b04a0880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0909a4c9f34f/disk-5df8b473.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/413a44ed225d/vmlinux-5df8b473.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c1d8ca...@syzkaller.appspotmail.com

================================================
WARNING: lock held when returning to user space!

4.14.293-syzkaller #0 Not tainted
------------------------------------------------
syz-executor121/7956 is leaving the kernel with locks still held!
1 lock held by syz-executor121/7956:
#0: (&lo->lo_ctl_mutex/1){+.+.}, at: [<ffffffff838da087>] lo_ioctl+0x87/0x1cd0 drivers/block/loop.c:1419