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? > > 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. > > Yes, it could be a new config option. This will be a useful feature that > I believe most distros will turn it on. Or we may just include that in > the core code without any option. Do we need another option? or just extend DETECT_HUNG_TASK? Thanks, > > BTW, this field can also be shared by other sleeping locks like rwsem > and rt_mutex as a task can only be blocked on one of them. We do need > another type field to identify the type of the blocked lock. > > Cheers, > Longman > > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
