linux-kernel - Re: [PATCH v2] perf lock contention: Change stack

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Message-ID: <ZrpHZ01AE3kwsh2x@x1>
Date: Mon, 12 Aug 2024 14:33:27 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Ian Rogers <irogers@...gle.com>, Kan Liang <kan.liang@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	linux-perf-users@...r.kernel.org,
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v2] perf lock contention: Change stack_id type to s32

On Mon, Aug 12, 2024 at 10:25:33AM -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")
> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> v2) fix build error for s32

Thanks, applied to perf-tools-next,

- Arnaldo
 
>  tools/perf/util/bpf_skel/lock_data.h       | 4 ++--
>  tools/perf/util/bpf_skel/vmlinux/vmlinux.h | 1 +
>  2 files changed, 3 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;
>  };
> diff --git a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> index e9028235d771..d818e30c5457 100644
> --- a/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> +++ b/tools/perf/util/bpf_skel/vmlinux/vmlinux.h
> @@ -15,6 +15,7 @@
>  
>  typedef __u8 u8;
>  typedef __u32 u32;
> +typedef __s32 s32;
>  typedef __u64 u64;
>  typedef __s64 s64;
>  
> -- 
> 2.46.0.76.ge559c4bf1a-goog