Re: [PATCH 3/8] rcu/exp: Fix RCU expedited parallel grace period kworker allocation failure recovery

Kalesh Singh
2023-12-12T16:11:12Z

On Tue, Dec 12, 2023 at 11:04 AM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> On Fri, Dec 8, 2023 at 5:06 PM Frederic Weisbecker <frederic@kernel.org> wrote:
> >
> > Under CONFIG_RCU_EXP_KTHREAD=y, the nodes initialization for expedited
> > grace periods is queued to a kworker. However if the allocation of that
> > kworker failed, the nodes initialization is performed synchronously by
> > the caller instead.
> >
> > Now the check for kworker initialization failure relies on the kworker
> > pointer to be NULL while its value might actually encapsulate an
> > allocation failure error.
> >
> > Make sure to handle this case.
> >
> > Fixes: 9621fbee44df ("rcu: Move expedited grace period (GP) work to RT kthread_worker")
> > Cc: Kalesh Singh <kaleshsingh@google.com>
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > ---
> > kernel/rcu/tree.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 82f8130d3fe3..055f4817bc70 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -4723,6 +4723,7 @@ static void __init rcu_start_exp_gp_kworkers(void)
> > rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
> > if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
> > pr_err("Failed to create %s!\n", par_gp_kworker_name);
> > + rcu_exp_par_gp_kworker = NULL;
> > kthread_destroy_worker(rcu_exp_gp_kworker);
>
> Hi Frederic,
>
> Thanks for catching this. I think we need to remove the
> kthread_destroy_worker() in this case too.

Ahh sorry, that's the other kworker. LGTM. Thanks.

>
> Otherwise,
>
> Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
>
> --Kalesh
>
> > return;
> > }
> > --
> > 2.42.1
> >