On Thu, May 02, 2024 at 11:05:01AM +0900, Masami Hiramatsu wrote:
> On Wed, 1 May 2024 16:12:37 -0700
> "Paul E. McKenney" <[email protected]> wrote:
>
> > Note that the immediate pressure for this patch should be relieved by the
> > NAPI patch series [1], but this sort of problem could easily arise again.
> >
> > When running heavy test workloads with KASAN enabled, RCU Tasks grace
> > periods can extend for many tens of seconds, significantly slowing
> > trace registration. Therefore, make the registration-side RCU Tasks
> > grace period be asynchronous via call_rcu_tasks().
>
> Good catch! AFAICS, there is no reason to wait for synchronization
> when adding a new direct trampoline.
> This looks good to me.
>
> Reviewed-by: Masami Hiramatsu (Google) <[email protected]>
Thank you very much! I will apply this on my next rebase.
Thanx, Paul
> Thank you,
>
> > [1] https://lore.kernel.org/all/[email protected]/
> >
> > Reported-by: Jakub Kicinski <[email protected]>
> > Reported-by: Alexei Starovoitov <[email protected]>
> > Reported-by: Chris Mason <[email protected]>
> > Signed-off-by: Paul E. McKenney <[email protected]>
> > Cc: Steven Rostedt <[email protected]>
> > Cc: Masami Hiramatsu <[email protected]>
> > Cc: Mark Rutland <[email protected]>
> > Cc: Mathieu Desnoyers <[email protected]>
> > Cc: <[email protected]>
> >
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 6c96b30f3d63b..32ea92934268c 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -5365,6 +5365,13 @@ static void remove_direct_functions_hash(struct
> > ftrace_hash *hash, unsigned long
> > }
> > }
> >
> > +static void register_ftrace_direct_cb(struct rcu_head *rhp)
> > +{
> > + struct ftrace_hash *fhp = container_of(rhp, struct ftrace_hash, rcu);
> > +
> > + free_ftrace_hash(fhp);
> > +}
> > +
> > /**
> > * register_ftrace_direct - Call a custom trampoline directly
> > * for multiple functions registered in @ops
> > @@ -5463,10 +5470,8 @@ int register_ftrace_direct(struct ftrace_ops *ops,
> > unsigned long addr)
> > out_unlock:
> > mutex_unlock(&direct_mutex);
> >
> > - if (free_hash && free_hash != EMPTY_HASH) {
> > - synchronize_rcu_tasks();
> > - free_ftrace_hash(free_hash);
> > - }
> > + if (free_hash && free_hash != EMPTY_HASH)
> > + call_rcu_tasks(&free_hash->rcu, register_ftrace_direct_cb);
> >
> > if (new_hash)
> > free_ftrace_hash(new_hash);
>
>
> --
> Masami Hiramatsu (Google) <[email protected]>
