[Cc Joel]
On Sun, Feb 23, 2025 at 08:43:10PM -0800, Boqun Feng wrote:
> The rcutorture_one_extend_check() function's second last check assumes
> that "preempt_count() & PREEMPT_MASK" is non-zero only if
> RCUTORTURE_RDR_PREEMPT or RCUTORTURE_RDR_SCHED bit is set.
>
> This works for preemptible RCU and for non-preemptible RCU running in
> a non-preemptible kernel. But it fails for non-preemptible RCU running
> in a preemptible kernel because then rcu_read_lock() is just
> preempt_disable(), which increases preempt count.
>
> This commit therefore adjusts this check to take into account the case
> fo non-preemptible RCU running in a preemptible kernel.
>
> Signed-off-by: Boqun Feng <[email protected]>
> ---
> kernel/rcu/rcutorture.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 280bff706017..4cae119dece8 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -1901,8 +1901,16 @@ static void rcutorture_one_extend_check(char *s, int
> curstate, int new, int old,
> WARN_ONCE(cur_ops->extendables &&
> !(curstate & (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH)) &&
> (preempt_count() & SOFTIRQ_MASK), ROEC_ARGS);
> - WARN_ONCE(cur_ops->extendables &&
> - !(curstate & (RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED))
> &&
> +
> + /*
> + * non-preemptible RCU in a preemptible kernel uses preempt_disable()
> + * as rcu_read_lock().
> + */
> + mask = RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED;
> + if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
> + mask |= RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2;
> +
> + WARN_ONCE(cur_ops->extendables && !(curstate & mask) &&
> (preempt_count() & PREEMPT_MASK), ROEC_ARGS);
>
> /*
> --
> 2.39.5 (Apple Git-154)
>
>
