[v6.6] WARNING: lock held when returning to user space in loop_set_block_size

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc1a1c5b404a Linux 6.6.103
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16a3bef0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=412020841cf033b0
dashboard link: https://syzkaller.appspot.com/bug?extid=53ce52a8070d96c8f320
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/46c06862a545/disk-cc1a1c5b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/38ddabb6fc8b/vmlinux-cc1a1c5b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b130b7d031b5/bzImage-cc1a1c5b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+53ce52...@syzkaller.appspotmail.com

================================================
WARNING: lock held when returning to user space!
syzkaller #0 Not tainted
------------------------------------------------
syz.2.159/6258 is leaving the kernel with locks still held!
1 lock held by syz.2.159/6258:
#0: ffff8880216bfb60 (&lo->lo_mutex){+.+.}-{3:3}, at: loop_set_block_size+0x7c/0x480 drivers/block/loop.c:1490


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: cc1a1c5b404a Linux 6.6.103
git tree: linux-6.6.y

console output: https://syzkaller.appspot.com/x/log.txt?x=109d81f0580000

kernel config: https://syzkaller.appspot.com/x/.config?x=412020841cf033b0
dashboard link: https://syzkaller.appspot.com/bug?extid=53ce52a8070d96c8f320
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=142b2a62580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=104d8e34580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/46c06862a545/disk-cc1a1c5b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/38ddabb6fc8b/vmlinux-cc1a1c5b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b130b7d031b5/bzImage-cc1a1c5b.xz

mounted in repro: https://storage.googleapis.com/syzbot-assets/441ee0ab0c2b/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+53ce52...@syzkaller.appspotmail.com

syz.0.17[5945]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
loop0: detected capacity change from 0 to 2048
loop0: p1 < > p3
loop0: p3 size 134217728 extends beyond EOD, truncated

================================================
WARNING: lock held when returning to user space!
syzkaller #0 Not tainted
------------------------------------------------

syz.0.17/5945 is leaving the kernel with locks still held!
1 lock held by syz.0.17/5945:
#0: ffff888140b49b60 (&lo->lo_mutex){+.+.}-{3:3}, at: loop_set_block_size+0x7c/0x480 drivers/block/loop.c:1490


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If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 42a6aeb4b23890a4d2323b51841690be7ea49f8d
Author: Eric Hagberg <ehag...@janestreet.com>
Date: Mon Sep 22 17:17:04 2025 +0000

Revert "loop: Avoid updating block size under exclusive owner"

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1605932f980000
start commit: 60a9e718726f Linux 6.6.106
git tree: linux-6.6.y
kernel config: https://syzkaller.appspot.com/x/.config?x=12606d4b8832c7e4
dashboard link: https://syzkaller.appspot.com/bug?extid=53ce52a8070d96c8f320
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11844f62580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=102aae42580000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: Revert "loop: Avoid updating block size under exclusive owner"

For information about bisection process see: https://goo.gl/tpsmEJ#bisection