Re: [PATCH] bcachefs: Mark bch_inode_info as SLAB_ACCOUNT

[Youling Tang <youling.tang@linux.dev>]

On 12/07/2024 08:03, Kent Overstreet wrote:
> On Wed, Jul 03, 2024 at 03:09:55PM GMT, Youling Tang wrote:
>> From: Youling Tang <tangyouling@kylinos.cn>
>>
>> After commit 230e9fc28604 ("slab: add SLAB_ACCOUNT flag"), we need to mark
>> the inode cache as SLAB_ACCOUNT, similar to commit 5d097056c9a0 ("kmemcg:
>> account for certain kmem allocations to memcg")
>>
>> Signed-off-by: Youling Tang <tangyouling@kylinos.cn>
> Turns out this was never tested with memcg enabled (!).
>
> I'm reverting it, please feel free to send me a fixed version.
Sorry, my oversight.

The following null pointer dereference is triggered after MEMCG 
configuration is enabled.
```
BUG: kernel NULL pointer dereference, address: 0000000000000008
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP
CPU: 5 PID: 1702 Comm: umount Not tainted 
6.10.0-rc7-ktest-00003-g557bd05b0d4c-dirty #12
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
RIP: 0010:list_lru_add+0x83/0x100
Code: 5f 5d c3 48 8b 45 d0 48 85 c0 74 13 41 80 7c 24 1c 00 48 63 b0 68 
06 00 00 74 04 85 f6 79 5e 4d 03 2c 24 49 83 c5 08 4c 89 ea <49> 8b 45 
08 49 89 5d 08 48 89 13 48 89 43 08 48 89 18 49 8b 45 10
RSP: 0018:ffff8881178efd10 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88810ec140f0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000017 RDI: ffff8881178efcc8
RBP: ffff8881178efd48 R08: ffff8881009de780 R09: ffffffff822e0de0
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888102075c80
R13: 0000000000000000 R14: ffff88810443e6c0 R15: 0000000000000000
FS:  00007f9ed1840800(0000) GS:ffff888179940000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000008 CR3: 00000001062b9005 CR4: 0000000000370eb0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:
  <TASK>
  ? show_regs+0x69/0x70
  ? __die+0x29/0x70
  ? page_fault_oops+0x14f/0x3c0
  ? do_user_addr_fault+0x2d0/0x5b0
  ? default_wake_function+0x1e/0x30
  ? exc_page_fault+0x6d/0x130
  ? asm_exc_page_fault+0x2b/0x30
  ? list_lru_add+0x83/0x100
  list_lru_add_obj+0x4b/0x60
  iput+0x1fe/0x220
  dentry_unlink_inode+0xbd/0x120
  __dentry_kill+0x78/0x180
  dput+0xc7/0x170
  shrink_dcache_for_umount+0xe8/0x120
  generic_shutdown_super+0x23/0x150
  bch2_kill_sb+0x1b/0x30
  deactivate_locked_super+0x34/0xb0
  deactivate_super+0x44/0x50
  cleanup_mnt+0x105/0x160
  __cleanup_mnt+0x16/0x20
  task_work_run+0x63/0x90
  syscall_exit_to_user_mode+0x10d/0x110
  do_syscall_64+0x57/0x100
  entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7f9ed1a7a6e7
Code: 0c 00 f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 31 f6 e9 
09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 
f0 ff ff 77 01 c3 48 8b 15 09 97 0c 00 f7 d8 64 89 02 b8
RSP: 002b:00007ffef8a29128 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 000055f4671acad8 RCX: 00007f9ed1a7a6e7
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000055f4671b1240
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9ed1bc6244
R13: 000055f4671b1240 R14: 000055f4671acde0 R15: 000055f4671ac9d0
  </TASK>
```

I'm going to analyze it.

Thanks,
Youling.