[syzbot ci] Re: blk-cgroup: protect blkgs with blkcg_mutex

syzbot ci has tested the following series

[v2] blk-cgroup: protect blkgs with blkcg_mutex
https://lore.kernel.org/all/[email protected]
* [RFC PATCH v2 1/8] block: associate blkg in submit_bio instead of bio_set_dev
* [RFC PATCH v2 2/8] blk-throttle: protect throttle state with td lock
* [RFC PATCH v2 3/8] blk-cgroup: protect blkgs with blkcg_mutex
* [RFC PATCH v2 4/8] blk-cgroup: remove blkg radix tree preloading
* [RFC PATCH v2 5/8] blk-cgroup: allocate blkgs in blkg_create
* [RFC PATCH v2 6/8] blk-cgroup: share blkg creation between lookup and config prep
* [RFC PATCH v2 7/8] bfq: avoid blkg lookup from locked cgroup update
* [RFC PATCH v2 8/8] block: fail nowait bio submit if blkg allocation can't sleep

and found the following issue:
general protection fault in blkcg_punt_bio_submit

Full report is available here:
https://ci.syzbot.org/series/eece31b0-1f5d-4840-8a12-407d9a4d1c57

***

general protection fault in blkcg_punt_bio_submit

tree:      axboe
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/axboe/linux.git
base:      093fbffe03f5c1bb9c10a9e5aa65b23250844403
arch:      amd64
compiler:  Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
config:    https://ci.syzbot.org/builds/2cc06765-4cf6-4329-9c0a-9fe326a5338e/config
syz repro: https://ci.syzbot.org/findings/38efdd1d-4179-4903-8ade-04afbce263b2/syz_repro

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000006: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000030-0x0000000000000037]
CPU: 0 UID: 0 PID: 26 Comm: kworker/u9:0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: btrfs-worker btrfs_work_helper
RIP: 0010:blkcg_punt_bio_submit+0x47/0x130 block/blk-cgroup.c:243
Code: ae 13 fd 4c 8d 73 50 4c 89 f0 48 c1 e8 03 80 3c 28 00 74 08 4c 89 f7 e8 07 06 7f fd 4d 8b 36 4d 8d 7e 30 4c 89 f8 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 ff e8 eb 05 7f fd 49 83 3f 00 0f 84 ab 00
RSP: 0000:ffffc90000a17a28 EFLAGS: 00010206
RAX: 0000000000000006 RBX: ffff888117071348 RCX: ffff8881032f5940
RDX: 0000000000000000 RSI: 0000000004000000 RDI: ffff888117071348
RBP: dffffc0000000000 R08: ffff8881bb74406f R09: 1ffff110376e880d
R10: dffffc0000000000 R11: ffffed10376e880e R12: ffff88816c5e6f08
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000030
FS:  0000000000000000(0000) GS:ffff88818d9cb000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f05d5660000 CR3: 0000000172eb2000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 run_ordered_work fs/btrfs/async-thread.c:243 [inline]
 btrfs_work_helper+0x577/0xc50 fs/btrfs/async-thread.c:322
 process_one_work kernel/workqueue.c:3314 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3397
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3478
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:blkcg_punt_bio_submit+0x47/0x130 block/blk-cgroup.c:243
Code: ae 13 fd 4c 8d 73 50 4c 89 f0 48 c1 e8 03 80 3c 28 00 74 08 4c 89 f7 e8 07 06 7f fd 4d 8b 36 4d 8d 7e 30 4c 89 f8 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 ff e8 eb 05 7f fd 49 83 3f 00 0f 84 ab 00
RSP: 0000:ffffc90000a17a28 EFLAGS: 00010206
RAX: 0000000000000006 RBX: ffff888117071348 RCX: ffff8881032f5940
RDX: 0000000000000000 RSI: 0000000004000000 RDI: ffff888117071348
RBP: dffffc0000000000 R08: ffff8881bb74406f R09: 1ffff110376e880d
R10: dffffc0000000000 R11: ffffed10376e880e R12: ffff88816c5e6f08
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000030
FS:  0000000000000000(0000) GS:ffff8882a8fcb000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007efceadf26a8 CR3: 0000000115190000 CR4: 00000000000006f0
----------------
Code disassembly (best guess):
   0:	ae                   	scas   %es:(%rdi),%al
   1:	13 fd                	adc    %ebp,%edi
   3:	4c 8d 73 50          	lea    0x50(%rbx),%r14
   7:	4c 89 f0             	mov    %r14,%rax
   a:	48 c1 e8 03          	shr    $0x3,%rax
   e:	80 3c 28 00          	cmpb   $0x0,(%rax,%rbp,1)
  12:	74 08                	je     0x1c
  14:	4c 89 f7             	mov    %r14,%rdi
  17:	e8 07 06 7f fd       	call   0xfd7f0623
  1c:	4d 8b 36             	mov    (%r14),%r14
  1f:	4d 8d 7e 30          	lea    0x30(%r14),%r15
  23:	4c 89 f8             	mov    %r15,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	80 3c 28 00          	cmpb   $0x0,(%rax,%rbp,1) <-- trapping instruction
  2e:	74 08                	je     0x38
  30:	4c 89 ff             	mov    %r15,%rdi
  33:	e8 eb 05 7f fd       	call   0xfd7f0623
  38:	49 83 3f 00          	cmpq   $0x0,(%r15)
  3c:	0f                   	.byte 0xf
  3d:	84                   	.byte 0x84
  3e:	ab                   	stos   %eax,%es:(%rdi)


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: [email protected]

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