[syzbot] [block?] possible deadlock in blkdev_buffered_write

[syzbot <syzbot+bd975ef54294bec73f0e@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    2efb7a11f1aa Add linux-next specific files for 20261016
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15344895580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=129fca4e65ab9877
dashboard link: https://syzkaller.appspot.com/bug?extid=bd975ef54294bec73f0e
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=110b0f01580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17b99031580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cd996cff1b76/disk-2efb7a11.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/59577d58bd5a/vmlinux-2efb7a11.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a3dfa3b04143/bzImage-2efb7a11.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/2b9971624b86/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+bd975ef54294bec73f0e@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.0.40/6005 is trying to acquire lock:
ffff888024956f68 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
ffff888024956f68 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: blkdev_buffered_write+0xd7/0x160 block/fops.c:738

but task is already holding lock:
ffff888024956f68 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
ffff888024956f68 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: blkdev_write_iter+0x6c5/0x810 block/fops.c:815

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&sb->s_type->i_mutex_key#10);
  lock(&sb->s_type->i_mutex_key#10);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

locks held by syz.0.40/6005: 1, last CPU#1:
 #0: ffff888024956f68 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: inode_lock_shared include/linux/fs.h:1039 [inline]
 #0: ffff888024956f68 (&sb->s_type->i_mutex_key#10){++++}-{4:4}, at: blkdev_write_iter+0x6c5/0x810 block/fops.c:815

stack backtrace:
CPU: 1 UID: 0 PID: 6005 Comm: syz.0.40 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_deadlock_bug+0x27a/0x290 kernel/locking/lockdep.c:3085
 check_deadlock kernel/locking/lockdep.c:3137 [inline]
 validate_chain kernel/locking/lockdep.c:3939 [inline]
 __lock_acquire+0x25db/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 down_read+0x45/0x320 kernel/locking/rwsem.c:1574
 inode_lock_shared include/linux/fs.h:1039 [inline]
 blkdev_buffered_write+0xd7/0x160 block/fops.c:738
 blkdev_write_iter+0x6d5/0x810 block/fops.c:816
 do_iter_readv_writev+0x612/0x8c0 fs/read_write.c:-1
 vfs_writev+0x343/0x990 fs/read_write.c:1768
 do_pwritev fs/read_write.c:1864 [inline]
 __do_sys_pwritev2 fs/read_write.c:1922 [inline]
 __se_sys_pwritev2+0x177/0x2a0 fs/read_write.c:1913
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff2f2b9e559
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff19d23ca8 EFLAGS: 00000246 ORIG_RAX: 0000000000000148
RAX: ffffffffffffffda RBX: 00007ff2f2e25fa0 RCX: 00007ff2f2b9e559
RDX: 0000000000000001 RSI: 0000200000000240 RDI: 0000000000000004
RBP: 00007ff2f2c35ab8 R08: 0000000000000000 R09: 0000000000000003
R10: 0000000000007a00 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff2f2e25fac R14: 00007ff2f2e25fa0 R15: 00007ff2f2e25fa0
 </TASK>


---
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