Re: [PATCH] perf lock contention: Change stack_id type to s32

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Sat, Aug 10, 2024 at 12:17:04PM -0700, Namhyung Kim wrote:
> The bpf_get_stackid() helper returns a signed type to check whether it
> failed to get a stacktrace or not.  But it saved the result in u32 and
> checked if the value is negative.
> 
>       376         if (needs_callstack) {
>       377                 pelem->stack_id = bpf_get_stackid(ctx, &stacks,
>       378                                                   BPF_F_FAST_STACK_CMP | stack_skip);
>   --> 379                 if (pelem->stack_id < 0)
> 
>   ./tools/perf/util/bpf_skel/lock_contention.bpf.c:379 contention_begin()
>   warn: unsigned 'pelem->stack_id' is never less than zero.
> 
> Let's change the type to s32 instead.
> 
> Fixes: 6d499a6b3d90 ("perf lock: Print the number of lost entries for BPF")

Thanks, applied to perf-tools-next,

- Arnaldo

> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/util/bpf_skel/lock_data.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/bpf_skel/lock_data.h b/tools/perf/util/bpf_skel/lock_data.h
> index 36af11faad03..de12892f992f 100644
> --- a/tools/perf/util/bpf_skel/lock_data.h
> +++ b/tools/perf/util/bpf_skel/lock_data.h
> @@ -7,11 +7,11 @@ struct tstamp_data {
>  	u64 timestamp;
>  	u64 lock;
>  	u32 flags;
> -	u32 stack_id;
> +	s32 stack_id;
>  };
>  
>  struct contention_key {
> -	u32 stack_id;
> +	s32 stack_id;
>  	u32 pid;
>  	u64 lock_addr_or_cgroup;
>  };
> -- 
> 2.46.0.76.ge559c4bf1a-goog