[syzbot] [bcachefs?] WARNING: suspicious RCU usage in bch2_snapshot_tree_oldest_subvol

[syzbot <syzbot+f7c41a878676b72c16a6@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    a430d95c5efa Merge tag 'lsm-pr-20240911' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11949d00580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1653f803fffa3848
dashboard link: https://syzkaller.appspot.com/bug?extid=f7c41a878676b72c16a6
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15c46a77980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13c1dc07980000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-a430d95c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/66a65abf87c4/vmlinux-a430d95c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/09c88015f9aa/bzImage-a430d95c.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/a2e2f261011a/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f7c41a878676b72c16a6@syzkaller.appspotmail.com

snapshot points to missing/incorrect tree:
  u64s 8 type snapshot 0:4294967295:0 len 0 ver 0: is_subvol 1 deleted 0 parent          0 children          0          0 subvol 1 tree 0, fixing
=============================
WARNING: suspicious RCU usage
6.11.0-syzkaller-02574-ga430d95c5efa #0 Not tainted
-----------------------------
fs/bcachefs/snapshot.h:45 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
3 locks held by syz-executor345/5099:
 #0: ffff888041400278 (&c->state_lock){+.+.}-{3:3}, at: bch2_fs_start+0x45/0x5b0 fs/bcachefs/super.c:1006
 #1: ffff8880414042c0 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:151 [inline]
 #1: ffff8880414042c0 (&c->btree_trans_barrier){.+.+}-{0:0}, at: srcu_read_lock include/linux/srcu.h:250 [inline]
 #1: ffff8880414042c0 (&c->btree_trans_barrier){.+.+}-{0:0}, at: __bch2_trans_get+0x7de/0xd20 fs/bcachefs/btree_iter.c:3200
 #2: ffff88801a898128 (bcachefs_btree){+.+.}-{0:0}, at: srcu_lock_acquire include/linux/srcu.h:151 [inline]
 #2: ffff88801a898128 (bcachefs_btree){+.+.}-{0:0}, at: srcu_read_lock include/linux/srcu.h:250 [inline]
 #2: ffff88801a898128 (bcachefs_btree){+.+.}-{0:0}, at: __bch2_trans_get+0x7de/0xd20 fs/bcachefs/btree_iter.c:3200

stack backtrace:
CPU: 0 UID: 0 PID: 5099 Comm: syz-executor345 Not tainted 6.11.0-syzkaller-02574-ga430d95c5efa #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:93 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119
 lockdep_rcu_suspicious+0x221/0x340 kernel/locking/lockdep.c:6724
 snapshot_t fs/bcachefs/snapshot.h:45 [inline]
 bch2_snapshot_tree_oldest_subvol+0x485/0x550 fs/bcachefs/snapshot.c:473
 snapshot_tree_ptr_repair fs/bcachefs/snapshot.c:714 [inline]
 check_snapshot fs/bcachefs/snapshot.c:836 [inline]
 bch2_check_snapshots+0x3f59/0x5320 fs/bcachefs/snapshot.c:889
 bch2_run_recovery_pass+0xf0/0x1e0 fs/bcachefs/recovery_passes.c:183
 bch2_run_recovery_passes+0x19e/0x820 fs/bcachefs/recovery_passes.c:230
 bch2_fs_recovery+0x24f9/0x38b0 fs/bcachefs/recovery.c:859
 bch2_fs_start+0x356/0x5b0 fs/bcachefs/super.c:1036
 bch2_fs_get_tree+0xd61/0x1700 fs/bcachefs/fs.c:1956
 vfs_get_tree+0x90/0x2b0 fs/super.c:1800
 do_new_mount+0x2be/0xb40 fs/namespace.c:3507
 do_mount fs/namespace.c:3847 [inline]
 __do_sys_mount fs/namespace.c:4055 [inline]
 __se_sys_mount+0x2d6/0x3c0 fs/namespace.c:4032
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7faacfc929ea
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 5e 04 00 00 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007faacfc47088 EFLAGS: 00000282 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007faacfc470a0 RCX: 00007faacfc929ea
RDX: 0000000020005d80 RSI: 0000000020005dc0 RDI: 00007faacfc470a0
RBP: 0000000000000004 R08: 00007faacfc470e0 R09: 0000000000005d77
R10: 0000000000000000 R11: 0000000000000282 R12: 00007faacfc470e0
R13: 0000000000000000 R14: 0000000000000003 R15: 0000000001000000
 </TASK>
 done
bcachefs (loop0): check_subvols... done
bcachefs (loop0): check_subvol_children... done
bcachefs (loop0): delete_dead_snapshots... done
bcachefs (loop0): check_inodes... done
bcachefs (loop0): check_extents... done
bcachefs (loop0): check_indirect_extents... done
bcachefs (loop0): check_dirents... done
bcachefs (loop0): check_xattrs... done
bcachefs (loop0): check_root... done
bcachefs (loop0): check_subvolume_structure... done
bcachefs (loop0): check_directory_structure... done
bcachefs (loop0): check_nlinks... done
bcachefs (loop0): resume_logged_ops... done
bcachefs (loop0): delete_dead_inodes... done
bcachefs (loop0): Fixed errors, running fsck a second time to verify fs is clean
bcachefs (loop0): check_alloc_info... done
bcachefs (loop0): check_lrus... done
bcachefs (loop0): check_btree_backpointers... done
bcachefs (loop0): check_backpointers_to_extents... done
bcachefs (loop0): check_extents_to_backpointers... done
bcachefs (loop0): check_alloc_to_lru_refs... done
bcachefs (loop0): check_snapshot_trees... done
bcachefs (loop0): check_snapshots... done
bcachefs (loop0): check_subvols... done
bcachefs (loop0): check_subvol_children... done
bcachefs (loop0): delete_dead_snapshots... done
bcachefs (loop0): check_inodes... done
bcachefs (loop0): check_extents... done
bcachefs (loop0): check_indirect_extents... done
bcachefs (loop0): check_dirents... done
bcachefs (loop0): check_xattrs... done
bcachefs (loop0): check_root... done
bcachefs (loop0): check_subvolume_structure... done
bcachefs (loop0): check_directory_structure... done
bcachefs (loop0): check_nlinks... done
bcachefs (loop0): resume_logged_ops... done
bcachefs (loop0): delete_dead_inodes... done
bcachefs (loop0): done starting filesystem
loop0: detected capacity change from 32768 to 32767
syz-executor345 (5099) used greatest stack depth: 12192 bytes left


---
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