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| author | Nikolay Kuratov <kniv@yandex-team.ru> | 2025-02-06 12:01:56 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-03-07 18:25:37 +0100 |
| commit | 746cc474a95473591853927b3a9792a2d671155b (patch) | |
| tree | 86aaeec2cc184e03864e224a78282bde4ef7da41 /kernel | |
| parent | 435d2964af815aae456db554c62963b4515f19d0 (diff) | |
| download | linux-746cc474a95473591853927b3a9792a2d671155b.tar.gz linux-746cc474a95473591853927b3a9792a2d671155b.tar.bz2 linux-746cc474a95473591853927b3a9792a2d671155b.zip | |
ftrace: Avoid potential division by zero in function_stat_show()
commit a1a7eb89ca0b89dc1c326eeee2596f263291aca3 upstream.
Check whether denominator expression x * (x - 1) * 1000 mod {2^32, 2^64}
produce zero and skip stddev computation in that case.
For now don't care about rec->counter * rec->counter overflow because
rec->time * rec->time overflow will likely happen earlier.
Cc: stable@vger.kernel.org
Cc: Wen Yang <wenyang@linux.alibaba.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250206090156.1561783-1-kniv@yandex-team.ru
Fixes: e31f7939c1c27 ("ftrace: Avoid potential division by zero in function profiler")
Signed-off-by: Nikolay Kuratov <kniv@yandex-team.ru>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/trace/ftrace.c | 27 |
1 files changed, 12 insertions, 15 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 71cc1bbfe9aa..dbd375f28ee0 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -541,6 +541,7 @@ static int function_stat_show(struct seq_file *m, void *v) static struct trace_seq s; unsigned long long avg; unsigned long long stddev; + unsigned long long stddev_denom; #endif mutex_lock(&ftrace_profile_lock); @@ -562,23 +563,19 @@ static int function_stat_show(struct seq_file *m, void *v) #ifdef CONFIG_FUNCTION_GRAPH_TRACER seq_puts(m, " "); - /* Sample standard deviation (s^2) */ - if (rec->counter <= 1) - stddev = 0; - else { - /* - * Apply Welford's method: - * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) - */ + /* + * Variance formula: + * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) + * Maybe Welford's method is better here? + * Divide only by 1000 for ns^2 -> us^2 conversion. + * trace_print_graph_duration will divide by 1000 again. + */ + stddev = 0; + stddev_denom = rec->counter * (rec->counter - 1) * 1000; + if (stddev_denom) { stddev = rec->counter * rec->time_squared - rec->time * rec->time; - - /* - * Divide only 1000 for ns^2 -> us^2 conversion. - * trace_print_graph_duration will divide 1000 again. - */ - stddev = div64_ul(stddev, - rec->counter * (rec->counter - 1) * 1000); + stddev = div64_ul(stddev, stddev_denom); } trace_seq_init(&s); |