[syzbot] [btrfs?] WARNING: suspicious RCU usage in btrfs_dev_name

[syzbot <syzbot+ba123cf1dd631315ffca@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    7d6661873f6b Add linux-next specific files for 20260226
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11591952580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=98a1e192f758c1c1
dashboard link: https://syzkaller.appspot.com/bug?extid=ba123cf1dd631315ffca
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4cd2824adb8a/disk-7d666187.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bbdd4a130d86/vmlinux-7d666187.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6e3bea3e96f8/bzImage-7d666187.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ba123cf1dd631315ffca@syzkaller.appspotmail.com

BTRFS info (device loop1): first mount of filesystem 7e32c2af-f87a-45a1-bcba-64dea7c56a53
BTRFS info (device loop1): using xxhash64 checksum algorithm
=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
fs/btrfs/volumes.h:872 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz.1.21/6007:
 #0: ffff8880346a60e0 (&type->s_umount_key#58/1){+.+.}-{4:4}, at: alloc_super+0x28c/0xab0 fs/super.c:345

stack backtrace:
CPU: 0 UID: 0 PID: 6007 Comm: syz.1.21 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 lockdep_rcu_suspicious+0x13f/0x1d0 kernel/locking/lockdep.c:6876
 btrfs_dev_name+0x128/0x130 fs/btrfs/volumes.h:872
 btrfs_repair_io_failure+0x4f8/0x6a0 fs/btrfs/bio.c:989
 btrfs_repair_eb_io_failure fs/btrfs/disk-io.c:198 [inline]
 btrfs_read_extent_buffer+0xb84/0xcd0 fs/btrfs/disk-io.c:245
 read_tree_block fs/btrfs/disk-io.c:592 [inline]
 read_tree_root_path+0x29d/0x840 fs/btrfs/disk-io.c:988
 load_global_roots_objectid+0x431/0xa20 fs/btrfs/disk-io.c:2095
 load_global_roots fs/btrfs/disk-io.c:2135 [inline]
 btrfs_read_roots fs/btrfs/disk-io.c:2160 [inline]
 init_tree_roots+0xbe2/0x2240 fs/btrfs/disk-io.c:2712
 open_ctree+0x1960/0x2e40 fs/btrfs/disk-io.c:3489
 btrfs_fill_super+0x187/0x2e0 fs/btrfs/super.c:981
 btrfs_get_tree_super fs/btrfs/super.c:1944 [inline]
 btrfs_get_tree_subvol fs/btrfs/super.c:2087 [inline]
 btrfs_get_tree+0xe77/0x1370 fs/btrfs/super.c:2121
 vfs_get_tree+0x92/0x2a0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3763 [inline]
 do_new_mount+0x341/0xd30 fs/namespace.c:3839
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4338
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f30d979da0a
Code: 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007f30da6dee58 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f30da6deee0 RCX: 00007f30d979da0a
RDX: 00002000000002c0 RSI: 0000200000000680 RDI: 00007f30da6deea0
RBP: 00002000000002c0 R08: 00007f30da6deee0 R09: 0000000001a001d8
R10: 0000000001a001d8 R11: 0000000000000246 R12: 0000200000000680
R13: 00007f30da6deea0 R14: 000000000002223e R15: 0000200000000000
 </TASK>
BTRFS info (device loop1): read error corrected: ino 0 off 30670848 (dev /dev/loop1 sector 76288)
BTRFS info (device loop1): read error corrected: ino 0 off 30687232 (dev /dev/loop1 sector 76320)
BTRFS info (device loop1): read error corrected: ino 0 off 30523392 (dev /dev/loop1 sector 76000)
BTRFS info (device loop1): read error corrected: ino 0 off 30457856 (dev /dev/loop1 sector 75872)
BTRFS info (device loop1): deleted orphan free space tree entries
BTRFS info (device loop1): checking UUID tree
BTRFS info (device loop1): turning on sync discard
BTRFS info (device loop1): enabling free space tree


---
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