Messages in this thread | | | Date | Mon, 10 Feb 2020 14:34:59 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] events: Annotate parent_ctx with __rcu |
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On Mon, Feb 10, 2020 at 06:29:48PM +0530, Amol Grover wrote: > On Mon, Feb 10, 2020 at 10:36:24AM +0100, Peter Zijlstra wrote: > > On Sat, Feb 08, 2020 at 08:16:49PM +0530, Amol Grover wrote:
> > > @@ -3106,26 +3106,31 @@ static void ctx_sched_out(struct perf_event_context *ctx, > > > static int context_equiv(struct perf_event_context *ctx1, > > > struct perf_event_context *ctx2) > > > { > > > + struct perf_event_context *parent_ctx1, *parent_ctx2; > > > + > > > lockdep_assert_held(&ctx1->lock); > > > lockdep_assert_held(&ctx2->lock); > > > > > > + parent_ctx1 = rcu_dereference(ctx1->parent_ctx); > > > + parent_ctx2 = rcu_dereference(ctx2->parent_ctx); > > > > Bah. > > > > Why are you fixing all this sparse crap and making the code worse? > > Hi Peter, > > Sparse is quite noisy and we need to eliminate false-positives, right?
Dunno, I've been happy just ignoring it all.
> __rcu will tell the developer, this pointer could change and he needs to > take the required steps to make sure the code doesn't break.
I know what it does; what I don't know is why you need to make the code worse. In paricular, __rcu doesn't mandate rcu_dereference(), esp. not when you're actually holding the write side lock.
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