[syzbot] [bcachefs?] general protection fault in check_init_srcu_struct

[syzbot <syzbot+747508948da55ff287c2@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    3d25a941ea50 Merge tag 'block-6.9-20240503' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=175e897f180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=45d8db3acdc1ccc6
dashboard link: https://syzkaller.appspot.com/bug?extid=747508948da55ff287c2
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: i386

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-3d25a941.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/49d9f26b0beb/vmlinux-3d25a941.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d2c424c14fff/bzImage-3d25a941.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+747508948da55ff287c2@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000031: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000188-0x000000000000018f]
CPU: 1 PID: 110 Comm: kswapd0 Not tainted 6.9.0-rc6-syzkaller-00227-g3d25a941ea50 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:check_init_srcu_struct+0x44/0x170 kernel/rcu/srcutree.c:408
Code: 53 48 89 fb 80 3c 02 00 0f 85 fe 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b 38 48 8d bd 88 01 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 ce 00 00 00 48 8b 85 88 01 00 00 a8 03 75 0b 5b
RSP: 0018:ffffc90001ef7568 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff888026f84240 RCX: ffffffff83ecf098
RDX: 0000000000000031 RSI: 0000000000000000 RDI: 0000000000000188
RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888026f84278
R13: ffff888064c22630 R14: 0000000000000000 R15: ffff888026f80000
FS:  0000000000000000(0000) GS:ffff88802c300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000562dfa8c9e28 CR3: 000000006730a000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 srcu_gp_start_if_needed+0x80/0xf00 kernel/rcu/srcutree.c:1221
 bkey_cached_free fs/bcachefs/btree_key_cache.c:90 [inline]
 bch2_btree_key_cache_scan+0xae0/0x1740 fs/bcachefs/btree_key_cache.c:893
 do_shrink_slab+0x44f/0x11c0 mm/shrinker.c:435
 shrink_slab+0x18a/0x1310 mm/shrinker.c:662
 shrink_one+0x493/0x7c0 mm/vmscan.c:4774
 shrink_many mm/vmscan.c:4835 [inline]
 lru_gen_shrink_node+0x89f/0x1750 mm/vmscan.c:4935
 shrink_node mm/vmscan.c:5894 [inline]
 kswapd_shrink_node mm/vmscan.c:6704 [inline]
 balance_pgdat+0x10d1/0x1a10 mm/vmscan.c:6895
 kswapd+0x5ea/0xbf0 mm/vmscan.c:7164
 kthread+0x2c1/0x3a0 kernel/kthread.c:388
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:check_init_srcu_struct+0x44/0x170 kernel/rcu/srcutree.c:408
Code: 53 48 89 fb 80 3c 02 00 0f 85 fe 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 6b 38 48 8d bd 88 01 00 00 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 ce 00 00 00 48 8b 85 88 01 00 00 a8 03 75 0b 5b
RSP: 0018:ffffc90001ef7568 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff888026f84240 RCX: ffffffff83ecf098
RDX: 0000000000000031 RSI: 0000000000000000 RDI: 0000000000000188
RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888026f84278
R13: ffff888064c22630 R14: 0000000000000000 R15: ffff888026f80000
FS:  0000000000000000(0000) GS:ffff88802c200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffed628afd8 CR3: 000000000d57a000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	53                   	push   %rbx
   1:	48 89 fb             	mov    %rdi,%rbx
   4:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
   8:	0f 85 fe 00 00 00    	jne    0x10c
   e:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  15:	fc ff df
  18:	48 8b 6b 38          	mov    0x38(%rbx),%rbp
  1c:	48 8d bd 88 01 00 00 	lea    0x188(%rbp),%rdi
  23:	48 89 fa             	mov    %rdi,%rdx
  26:	48 c1 ea 03          	shr    $0x3,%rdx
* 2a:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1) <-- trapping instruction
  2e:	0f 85 ce 00 00 00    	jne    0x102
  34:	48 8b 85 88 01 00 00 	mov    0x188(%rbp),%rax
  3b:	a8 03                	test   $0x3,%al
  3d:	75 0b                	jne    0x4a
  3f:	5b                   	pop    %rbx


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