linux-kernel - Re: [syzbot] [kernel?] KCSAN: data-race in pcpu_alloc_noprof / pcpu_balance

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Message-ID: <87le0a797h.ffs@tglx>
Date: Mon, 02 Sep 2024 10:26:10 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: syzbot <syzbot+6d392a44667baa45bb5a@...kaller.appspotmail.com>,
 linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
 x86@...nel.org, linux-mm@...ck.org
Subject: Re: [syzbot] [kernel?] KCSAN: data-race in pcpu_alloc_noprof /
 pcpu_balance_workfn (2)

On Thu, Aug 29 2024 at 09:53, syzbot wrote:

Cc-: x86 folks. Just because something happens on x86 does not mean it's
     an x86 problem

Cc+: mm folks. It's entirely clear where this belongs to:

> read-write to 0xffffffff88bb27ac of 4 bytes by task 3354 on cpu 0:
>  pcpu_update_empty_pages mm/percpu.c:602 [inline]

No?

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    d5d547aa7b51 Merge tag 'random-6.11-rc6-for-linus' of git:..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=164c067b980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=6fafac02e339cc84
> dashboard link: https://syzkaller.appspot.com/bug?extid=6d392a44667baa45bb5a
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/e636aa58c364/disk-d5d547aa.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f5ecd0d96afa/vmlinux-d5d547aa.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/fe7d474f148f/bzImage-d5d547aa.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+6d392a44667baa45bb5a@...kaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in pcpu_alloc_noprof / pcpu_balance_workfn
>
> read-write to 0xffffffff88bb27ac of 4 bytes by task 3354 on cpu 0:
>  pcpu_update_empty_pages mm/percpu.c:602 [inline]
>  pcpu_chunk_populated mm/percpu.c:1531 [inline]
>  pcpu_balance_populated mm/percpu.c:2062 [inline]
>  pcpu_balance_workfn+0x94e/0xa60 mm/percpu.c:2212
>  process_one_work kernel/workqueue.c:3231 [inline]
>  process_scheduled_works+0x483/0x9a0 kernel/workqueue.c:3312
>  worker_thread+0x526/0x6e0 kernel/workqueue.c:3389
>  kthread+0x1d1/0x210 kernel/kthread.c:389
>  ret_from_fork+0x4b/0x60 arch/x86/kernel/process.c:147
>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
>
> read to 0xffffffff88bb27ac of 4 bytes by task 6821 on cpu 1:
>  pcpu_alloc_noprof+0x9a7/0x10c0 mm/percpu.c:1894
>  bpf_map_alloc_percpu+0xad/0x210 kernel/bpf/syscall.c:466
>  prealloc_init+0x19f/0x470 kernel/bpf/hashtab.c:341
>  htab_map_alloc+0x630/0x8e0 kernel/bpf/hashtab.c:576
>  map_create+0x83c/0xb90 kernel/bpf/syscall.c:1333
>  __sys_bpf+0x667/0x7a0 kernel/bpf/syscall.c:5692
>  __do_sys_bpf kernel/bpf/syscall.c:5817 [inline]
>  __se_sys_bpf kernel/bpf/syscall.c:5815 [inline]
>  __x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5815
>  x64_sys_call+0x2625/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:322
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> value changed: 0x00000001 -> 0x00000004
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 UID: 0 PID: 6821 Comm: syz.4.1651 Not tainted 6.11.0-rc5-syzkaller-00081-gd5d547aa7b51 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024
> ==================================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> If the report is already addressed, let syzbot know by replying with:
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>
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>
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>
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