Re: [PATCH v2 bpf-next 1/4] perf: export get/put_chain_entry()

[Song Liu]

> On Jun 26, 2020, at 4:00 AM, Peter Zijlstra <pet...@infradead.org> wrote:
> 
> On Thu, Jun 25, 2020 at 05:13:29PM -0700, Song Liu wrote:
>> This would be used by bpf stack mapo.
> 
> Would it make sense to sanitize the API a little before exposing it?

I will fold this in the next version. 

Thanks,
Song

> 
> diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
> index 334d48b16c36..016894b0d2c2 100644
> --- a/kernel/events/callchain.c
> +++ b/kernel/events/callchain.c
> @@ -159,8 +159,10 @@ static struct perf_callchain_entry 
> *get_callchain_entry(int *rctx)
>               return NULL;
> 
>       entries = rcu_dereference(callchain_cpus_entries);
> -     if (!entries)
> +     if (!entries) {
> +             put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
>               return NULL;
> +     }
> 
>       cpu = smp_processor_id();
> 
> @@ -183,12 +185,9 @@ get_perf_callchain(struct pt_regs *regs, u32 init_nr, 
> bool kernel, bool user,
>       int rctx;
> 
>       entry = get_callchain_entry(&rctx);
> -     if (rctx == -1)
> +     if (!entry || rctx == -1)
>               return NULL;
> 
> -     if (!entry)
> -             goto exit_put;
> -
>       ctx.entry     = entry;
>       ctx.max_stack = max_stack;
>       ctx.nr        = entry->nr = init_nr;