* Re: [PATCH] perf lock contention: Reject more than 10ms delays for safety
2025-05-15 18:10 [PATCH] perf lock contention: Reject more than 10ms delays for safety Namhyung Kim
@ 2025-05-15 18:18 ` Ian Rogers
2025-05-31 11:45 ` Arnaldo Carvalho de Melo
2025-05-31 11:49 ` Arnaldo Carvalho de Melo
2 siblings, 0 replies; 4+ messages in thread
From: Ian Rogers @ 2025-05-15 18:18 UTC (permalink / raw)
To: Namhyung Kim
Cc: Arnaldo Carvalho de Melo, Kan Liang, Jiri Olsa, Adrian Hunter,
Peter Zijlstra, Ingo Molnar, LKML, linux-perf-users, Song Liu,
bpf, Alexei Starovoitov
Nit, in the subject line for clarity perhaps rather than "perf lock
contention:" call it "perf lock contention/delay" or "perf lock
delay".
On Thu, May 15, 2025 at 11:10 AM Namhyung Kim <namhyung@kernel.org> 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@cgroup_mutex true
> lock delay is too long: 100000us (> 10ms)
>
> Usage: perf lock contention [<options>]
>
> -J, --inject-delay <TIME@FUNC>
> Inject delays to specific locks
>
> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Namhyung Kim <namhyung@kernel.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) {
nit: It's unfortunate the variable name isn't carrying the time unit.
For example, this could be:
```
if (duration_ns > 10 * NSEC_PER_SEC) {
```
which should hopefully make it clearer what the time units are and
that they aren't messed up.
Thanks,
Ian
> + pr_err("lock delay is too long: %s (> 10ms)\n", spec);
> + return false;
> + }
> +
> tmp = realloc(delays, (nr_delays + 1) * sizeof(*delays));
> if (tmp == NULL) {
> pr_err("Memory allocation failure\n");
> --
> 2.49.0.1101.gccaa498523-goog
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] perf lock contention: Reject more than 10ms delays for safety
2025-05-15 18:10 [PATCH] perf lock contention: Reject more than 10ms delays for safety Namhyung Kim
2025-05-15 18:18 ` Ian Rogers
@ 2025-05-31 11:45 ` Arnaldo Carvalho de Melo
2025-05-31 11:49 ` Arnaldo Carvalho de Melo
2 siblings, 0 replies; 4+ messages in thread
From: Arnaldo Carvalho de Melo @ 2025-05-31 11:45 UTC (permalink / raw)
To: Namhyung Kim
Cc: Ian Rogers, Kan Liang, Jiri Olsa, Adrian Hunter, Peter Zijlstra,
Ingo Molnar, LKML, linux-perf-users, Song Liu, bpf,
Alexei Starovoitov
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@cgroup_mutex true
> lock delay is too long: 100000us (> 10ms)
>
> Usage: perf lock contention [<options>]
>
> -J, --inject-delay <TIME@FUNC>
> Inject delays to specific locks
>
> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Thanks, applied to perf-tools-next,
- Arnaldo
> ---
> 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;
> + }
> +
> tmp = realloc(delays, (nr_delays + 1) * sizeof(*delays));
> if (tmp == NULL) {
> pr_err("Memory allocation failure\n");
> --
> 2.49.0.1101.gccaa498523-goog
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] perf lock contention: Reject more than 10ms delays for safety
2025-05-15 18:10 [PATCH] perf lock contention: Reject more than 10ms delays for safety Namhyung Kim
2025-05-15 18:18 ` Ian Rogers
2025-05-31 11:45 ` Arnaldo Carvalho de Melo
@ 2025-05-31 11:49 ` Arnaldo Carvalho de Melo
2 siblings, 0 replies; 4+ messages in thread
From: Arnaldo Carvalho de Melo @ 2025-05-31 11:49 UTC (permalink / raw)
To: Namhyung Kim
Cc: Ian Rogers, Kan Liang, Jiri Olsa, Adrian Hunter, Peter Zijlstra,
Ingo Molnar, LKML, linux-perf-users, Song Liu, bpf,
Alexei Starovoitov
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@cgroup_mutex true
> lock delay is too long: 100000us (> 10ms)
>
> Usage: perf lock contention [<options>]
>
> -J, --inject-delay <TIME@FUNC>
> Inject delays to specific locks
>
> Suggested-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Namhyung Kim <namhyung@kernel.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
^ permalink raw reply [flat|nested] 4+ messages in thread