On Fri, 10 Apr 2026 at 14:20, Thomas Gleixner <[email protected]> wrote: > > KCSAN uses get_cycles() for two purposes: > > 1) Seeding the random state with get_cycles() is a historical leftover. > > 2) The microbenchmark uses get_cycles(), which provides an unit less > counter value and is not guaranteed to be functional on all > systems/platforms. > > Use random_get_entropy() for seeding the random state and ktime_get() which > is universaly functional and provides at least a comprehensible unit. > > This is part of a larger effort to remove get_cycles() usage from > non-architecture code. > > Signed-off-by: Thomas Gleixner <[email protected]> > Cc: Marco Elver <[email protected]> > Cc: Dmitry Vyukov <[email protected]> > Cc: [email protected]
Reviewed-by: Marco Elver <[email protected]> > --- > kernel/kcsan/core.c | 2 +- > kernel/kcsan/debugfs.c | 8 ++++---- > 2 files changed, 5 insertions(+), 5 deletions(-) > > --- a/kernel/kcsan/core.c > +++ b/kernel/kcsan/core.c > @@ -798,7 +798,7 @@ void __init kcsan_init(void) > BUG_ON(!in_task()); > > for_each_possible_cpu(cpu) > - per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles(); > + per_cpu(kcsan_rand_state, cpu) = (u32)random_get_entropy(); > > /* > * We are in the init task, and no other tasks should be running; > --- a/kernel/kcsan/debugfs.c > +++ b/kernel/kcsan/debugfs.c > @@ -58,7 +58,7 @@ static noinline void microbenchmark(unsi > { > const struct kcsan_ctx ctx_save = current->kcsan_ctx; > const bool was_enabled = READ_ONCE(kcsan_enabled); > - u64 cycles; > + ktime_t nsecs; > > /* We may have been called from an atomic region; reset context. */ > memset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx)); > @@ -70,16 +70,16 @@ static noinline void microbenchmark(unsi > > pr_info("%s begin | iters: %lu\n", __func__, iters); > > - cycles = get_cycles(); > + nsecs = ktime_get(); > while (iters--) { > unsigned long addr = iters & ((PAGE_SIZE << 8) - 1); > int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC : > (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0); > __kcsan_check_access((void *)addr, sizeof(long), type); > } > - cycles = get_cycles() - cycles; > + nsecs = ktime_get() - nsecs; > > - pr_info("%s end | cycles: %llu\n", __func__, cycles); > + pr_info("%s end | nsecs: %llu\n", __func__, nsecs); > > WRITE_ONCE(kcsan_enabled, was_enabled); > /* restore context */ >
