Re: [PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Peter Zijlstra]

On Mon, Sep 07, 2026 at 11:53:51AM -0400, Gregory Price wrote:
> On Mon, Sep 07, 2026 at 04:13:31PM +0800, Ye Liu wrote:
> > From: Ye Liu <liuye@xxxxxxxxxx>
> > 
> > Replace the manual rcu_read_lock()/rcu_read_unlock() and guard(rcu)
> > pairs combined with for_each_process(), for_each_thread() and
> > for_each_process_thread() loops across kernel/ with the
> > for_each_*_rculock() macros, which scope the RCU read lock to the
> > loop body via scoped_guard(rcu).
> > 
> > No functional change.
> > 
> > Signed-off-by: Ye Liu <liuye@xxxxxxxxxx>
> > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> 
> Question below
> 
> > diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> > index 6fcc94ce4ca9..73a5ad3be9a8 100644
> > --- a/kernel/hung_task.c
> > +++ b/kernel/hung_task.c
> > @@ -315,13 +315,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
> >  		return;
> >  
> >  	this_round_count = 0;
> > -	rcu_read_lock();
> > -	for_each_process_thread(g, t) {
> > +	for_each_process_thread_rculock(g, t) {
> >  		if (!max_count--)
> > -			goto unlock;
> > +			goto out;
> ... snip ...
> > - unlock:
> > -	rcu_read_unlock();
> > -
> > +out:
> >  	if (!this_round_count)
> >  		return;
> >  
> 
> The sunken rcu_read_lock()/unlock() + scoped_guard usage makes this goto
> at a minimum very confusing, if not actually broken.

You can use goto to exit a scope, that's fine. Using goto to enter a
scope is not (clang will error on that).

Just don't use computed goto, that goes sideways real quick.