Re: [PATCH 1/2] hung_task: Show the blocker task if the task is hung on mutex

[Waiman Long]

On 2/19/25 5:56 PM, Masami Hiramatsu (Google) wrote:
> On Wed, 19 Feb 2025 17:44:11 -0500
> Waiman Long <llong@xxxxxxxxxx> wrote:
>
> > On 2/19/25 3:24 PM, Steven Rostedt wrote:
> > > On Wed, 19 Feb 2025 15:18:57 -0500
> > > Waiman Long <llong@xxxxxxxxxx> wrote:
> > >
> > > > It is tricky to access the mutex_waiter structure which is allocated
> > > > from stack. So another way to work around this issue is to add a new
> > > > blocked_on_mutex field in task_struct to directly point to relevant
> > > > mutex. Yes, that increase the size of task_struct by 8 bytes, but it is
> > > > a pretty large structure anyway. Using READ_ONCE/WRITE_ONCE() to access
> > > And it's been on my TODO list for some time to try to make that structure
> > > smaller again :-/
> I agree to add the field, actually it was my first prototype :)
>
> > > > this field, we don't need to take lock, though taking the wait_lock may
> > > > still be needed to examine other information inside the mutex.
> Do we need to take it just for accessing owner, which is in an atomic?

Right. I forgot it is an atomic_long_t. In that case, no lock should be 
needed.

Cheers,
Longman