Re: [moderation/CI] Re: blk-cgroup: protect blkgs with blkcg_mutex

#syz upstream

On Sun, Jul 26, 2026 at 1:30 AM syzbot ci
<[email protected]> wrote:
>
> 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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