On Wed, 19 Feb 2025 15:24:35 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> 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 :-/
>
> > 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.
So something like this?
unsigned int block_flags;
union {
struct mutex *mutex;
struct rwsem +rwsem;
struct rtmutex *rtmutex;
} blocked_on;
enum {
BLOCKED_ON_MUTEX;
BLOCKED_ON_RWSEM;
BLOCKED_ON_RTMUTEX;
BLOCKED_ON_IO;
} block_reason;
For the safety, we may anyway lock the task anyway, but that is the
same as stacktrace.
Thank you,
>
> -- Steve
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
