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);
 		return;
 	}
-- 
2.42.1

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.

Otherwise,

Reviewed-by: Kalesh Singh <kaleshsingh@google.com>

--Kalesh

>                 return;
>         }
> --
> 2.42.1
>

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
> >