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

[Steven Rostedt]

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 :-/

> 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.

But perhaps if we add a new config option for this feature, we could just
add the lock that a task is blocked on before it goes to sleep and
reference that instead. That would be easier than trying to play games
getting the lock owner from the blocked_on field.

-- Steve