On Thu, 26 May 2022 16:49:26 +0200 Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > On Thu, May 26, 2022 at 11:25:30PM +0900, Masami Hiramatsu wrote: > > 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? > > sure I'll test it.. can't see the original email, > perhaps I wasn't cc-ed.. but I'll find it Here it is. I Cc-ed your @kernel.org address. https://lore.kernel.org/all/165189881197.175864.14757002789194211860.stgit@devnote2/T/#u > > is this also related to tracing 'idle' functions, > as discussed in here? > https://lore.kernel.org/bpf/20220515203653.4039075-1-jolsa@xxxxxxxxxx/ Ah, yes. So this may not happen with the above patch, but for the hardening (ensuring it is always safe), I would like to add this. > > because that's the one I can reproduce.. but I can > certainly try that with your change as well Thank you! > > jirka > > > > > 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> -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
