Re: WARNING in debug_mutex_unlock

[Hao Sun]

> On 13 Jan 2023, at 2:45 PM, Yonghong Song <yhs@xxxxxxxx> 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'")


> 
> 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);
>