2021-05-16 10:26:52

by Xu, Yanfei

Subject: [PATCH] rcu: fix a deadlock caused by not release rcu_node->lock

From: Yanfei Xu <[email protected]>

rcu_node->lock isn't released in rcu_print_task_stall() if the rcu_node
don't contain tasks which blocking the GP. However this rcu_node->lock
will be used again in rcu_dump_cpu_stacks() soon while the ndetected is
non-zero. As a result the cpu will hung by this deadlock.

Signed-off-by: Yanfei Xu <[email protected]>
---
kernel/rcu/tree_stall.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index b72311d24a9f..4e97c9977d1c 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -267,8 +267,10 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
struct task_struct *ts[8];

lockdep_assert_irqs_disabled();
- if (!rcu_preempt_blocked_readers_cgp(rnp))
+ if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
return 0;
+ }
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
rnp->level, rnp->grplo, rnp->grphi);
t = list_entry(rnp->gp_tasks->prev,
--
2.27.0

2021-05-16 15:57:02

by Xu, Yanfei

Subject: Re: [PATCH] rcu: fix a deadlock caused by not release rcu_node->lock

sorry, please ignore this patch...

Regards,
Yanfei

On 5/16/21 5:28 PM, [email protected] wrote:
> From: Yanfei Xu <[email protected]>
>
> rcu_node->lock isn't released in rcu_print_task_stall() if the rcu_node
> don't contain tasks which blocking the GP. However this rcu_node->lock
> will be used again in rcu_dump_cpu_stacks() soon while the ndetected is
> non-zero. As a result the cpu will hung by this deadlock.
>
> Signed-off-by: Yanfei Xu <[email protected]>
> ---
> kernel/rcu/tree_stall.h | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index b72311d24a9f..4e97c9977d1c 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -267,8 +267,10 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
> struct task_struct *ts[8];
>
> lockdep_assert_irqs_disabled();
> - if (!rcu_preempt_blocked_readers_cgp(rnp))
> + if (!rcu_preempt_blocked_readers_cgp(rnp)) {
> + raw_spin_lock_irqsave_rcu_node(rnp, flags);
> return 0;
> + }
> pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
> rnp->level, rnp->grplo, rnp->grphi);
> t = list_entry(rnp->gp_tasks->prev,
>