Re: WARNING in debug_mutex_unlock

[Yonghong Song]

On 1/15/23 6:24 PM, Hao Sun wrote:
> > 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'")

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);