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Message-ID: <0d2075a1-74df-96fc-ae42-3c9e10daab2a@meta.com>
Date:   Mon, 16 Jan 2023 22:02:37 -0800
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Subject: Re: WARNING in debug_mutex_unlock
To:     Hao Sun <sunhao.th@gmail.com>
Cc:     bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        David Miller <davem@davemloft.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20230109074425.12556-1-sunhao.th@gmail.com>
 <be494ee3-864d-1a33-e14d-d27712ab6248@meta.com>
 <C4BBA1C3-C704-49D3-8E13-18875B27FB47@gmail.com>
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From:   Yonghong Song <yhs@meta.com>
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On 1/15/23 6:24 PM, Hao Sun wrote:
> 
> 
>> On 13 Jan 2023, at 2:45 PM, Yonghong Song <yhs@meta.com> wrote:
>>
>>
>>
>> On 1/8/23 11:44 PM, Hao Sun wrote:
>>> Hi,
>>> The following warning can be triggered with the C reproducer in
>>> the link. The repro starts 32 threads, each attaches a tracepoint
>>> into `ext4_mark_inode_dirty`. The prog loads the following insns
>>> that simply sends signal to current proc, and then wait.
>>> Seems issues in queued irq_work with `do_bpf_send_signal`, also
>>> I'm wondering what if the task in `send_signal_irq_work` exited,
>>> at the time the callback invoked.
>>
>> Somehow, I cannot reproduce the issue in my qemu environment
>> with below kernel config and C reproducer.
>>
>> But could you try the following patch to see whether it
>> fixed the issue in your environment?
> 
> Tested the below patch on my local machine, seems fixed the issue.
> 
> Before applying the patch, the reproducer can still trigger the
> reported issue on a latest bpf-next build; After applying the
> patch, the warning no longer appears.
> 
> The test is conducted on: dfff86f8eb6a (“Merge branch 'samples/bpf:
> modernize BPF functionality test programs'")

Thanks for testing. I will submit a patch shortly with your
Reported-by and Tested-by.

> 
> 
>>
>> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
>> index 23ce498bca97..1b26d51caf31 100644
>> --- a/kernel/trace/bpf_trace.c
>> +++ b/kernel/trace/bpf_trace.c
>> @@ -831,6 +831,7 @@ static void do_bpf_send_signal(struct irq_work *entry)
>>
>>         work = container_of(entry, struct send_signal_irq_work, irq_work);
>>         group_send_sig_info(work->sig, SEND_SIG_PRIV, work->task, work->type);
>> +       put_task_struct(work->task);
>> }
>>
>> static int bpf_send_signal_common(u32 sig, enum pid_type type)
>> @@ -862,7 +863,7 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type)
>>                  * to the irq_work. The current task may change when queued
>>                  * irq works get executed.
>>                  */
>> -               work->task = current;
>> +               work->task = get_task_struct(current);
>>                 work->sig = sig;
>>                 work->type = type;
>>                 irq_work_queue(&work->irq_work);
>>
>