On Tue, 24 May 2022 19:23:01 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> On Sat, 7 May 2022 13:46:52 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> Is this expected to go through the BPF tree?
>
Yes, since rethook (fprobe) is currently used only from eBPF.
Jiri, can you check this is good for your test case?
Thank you,
> -- Steve
>
>
> > Since the rethook_recycle() will involve the call_rcu() for reclaiming
> > the rethook_instance, the rethook must be set up at the RCU available
> > context (non idle). This rethook_recycle() in the rethook trampoline
> > handler is inevitable, thus the RCU available check must be done before
> > setting the rethook trampoline.
> >
> > This adds a rcu_is_watching() check in the rethook_try_get() so that
> > it will return NULL if it is called when !rcu_is_watching().
> >
> > Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
> > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > ---
> > kernel/trace/rethook.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> > index b56833700d23..c69d82273ce7 100644
> > --- a/kernel/trace/rethook.c
> > +++ b/kernel/trace/rethook.c
> > @@ -154,6 +154,15 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
> > if (unlikely(!handler))
> > return NULL;
> >
> > + /*
> > + * This expects the caller will set up a rethook on a function entry.
> > + * When the function returns, the rethook will eventually be reclaimed
> > + * or released in the rethook_recycle() with call_rcu().
> > + * This means the caller must be run in the RCU-availabe context.
> > + */
> > + if (unlikely(!rcu_is_watching()))
> > + return NULL;
> > +
> > fn = freelist_try_get(&rh->pool);
> > if (!fn)
> > return NULL;
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
