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Message-ID: <aDrswP62_-fy3vUC@x1>
Date: Sat, 31 May 2025 08:49:20 -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, Song Liu <song@...nel.org>,
bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH] perf lock contention: Reject more than 10ms delays for
safety
On Thu, May 15, 2025 at 11:10:42AM -0700, Namhyung Kim wrote:
> Delaying kernel operations can be dangerous and the kernel may kill
> (non-sleepable) BPF programs running for long in the future.
>
> Limit the max delay to 10ms and update the document about it.
>
> $ sudo ./perf lock con -abl -J 100000us@...oup_mutex true
> lock delay is too long: 100000us (> 10ms)
>
> Usage: perf lock contention [<options>]
>
> -J, --inject-delay <TIME@...C>
> Inject delays to specific locks
>
> Suggested-by: Alexei Starovoitov <ast@...nel.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> tools/perf/Documentation/perf-lock.txt | 8 ++++++--
> tools/perf/builtin-lock.c | 5 +++++
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/Documentation/perf-lock.txt b/tools/perf/Documentation/perf-lock.txt
> index 2d9aecf630422aa6..c17b3e318169f9dc 100644
> --- a/tools/perf/Documentation/perf-lock.txt
> +++ b/tools/perf/Documentation/perf-lock.txt
> @@ -224,8 +224,12 @@ CONTENTION OPTIONS
> only with -b/--use-bpf.
>
> The 'time' is specified in nsec but it can have a unit suffix. Available
> - units are "ms" and "us". Note that it will busy-wait after it gets the
> - lock. Please use it at your own risk.
> + units are "ms", "us" and "ns". Currently it accepts up to 10ms of delays
> + for safety reasons.
> +
> + Note that it will busy-wait after it gets the lock. Delaying locks can
> + have significant consequences including potential kernel crashes. Please
> + use it at your own risk.
>
>
> SEE ALSO
> diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c
> index 41f6f3d2b779b986..3b3ade7a39cad01f 100644
> --- a/tools/perf/builtin-lock.c
> +++ b/tools/perf/builtin-lock.c
> @@ -2537,6 +2537,11 @@ static bool add_lock_delay(char *spec)
> return false;
> }
>
> + if (duration > 10 * 1000 * 1000) {
> + pr_err("lock delay is too long: %s (> 10ms)\n", spec);
> + return false;
> + }
> +
Please consider to replace those 1000 * 1000 her and in other places
with NSEC_PER_MSEC in a followup patch for the next merge window.
- Arnaldo
> tmp = realloc(delays, (nr_delays + 1) * sizeof(*delays));
> if (tmp == NULL) {
> pr_err("Memory allocation failure\n");
> --
> 2.49.0.1101.gccaa498523-goog
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