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Message-ID: <ZrozwIQcB_viRsKt@x1>
Date: Mon, 12 Aug 2024 13:09:36 -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] perf lock contention: Change stack_id type to s32
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@...aro.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.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
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