[PATCH] sched/core: add rcu_read_lock/unlock() protection

[PATCH] sched/core: add rcu_read_lock/unlock() protection

[qiang.zhang]

From: Zqiang <qiang.zhang@windriver.com>

Due to for_each_process_thread belongs to RCU read operation,
need to add rcu_read_lock/unlock() protection.

Signed-off-by: Zqiang <qiang.zhang@windriver.com>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8c5481077c9c..c3f0103fdf53 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7738,6 +7738,7 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
 	lockdep_assert_held(&rq->lock);
 
 	printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);
+	rcu_read_lock();
 	for_each_process_thread(g, p) {
 		if (task_cpu(p) != cpu)
 			continue;
@@ -7747,6 +7748,7 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
 
 		printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
 	}
+	rcu_read_unlock();
 }
 
 int sched_cpu_dying(unsigned int cpu)
-- 
2.17.1

Re: [PATCH] sched/core: add rcu_read_lock/unlock() protection

[Peter Zijlstra]

On Tue, Jan 26, 2021 at 04:46:51PM +0800, qiang.zhang@windriver.com wrote:
> From: Zqiang <qiang.zhang@windriver.com>
> 
> Due to for_each_process_thread belongs to RCU read operation,
> need to add rcu_read_lock/unlock() protection.
> 
> Signed-off-by: Zqiang <qiang.zhang@windriver.com>
> ---
>  kernel/sched/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 8c5481077c9c..c3f0103fdf53 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -7738,6 +7738,7 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
>  	lockdep_assert_held(&rq->lock);
>  
>  	printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);
> +	rcu_read_lock();
>  	for_each_process_thread(g, p) {
>  		if (task_cpu(p) != cpu)
>  			continue;
> @@ -7747,6 +7748,7 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
>  
>  		printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
>  	}
> +	rcu_read_unlock();

We're in stop machine, with IRQs disabled, please explain how this can
make any difference?

回复: [PATCH] sched/core: add rcu_read_lock/unlock() protection

[Zhang, Qiang]

________________________________________
发件人: Zhang, Qiang <qiang.zhang@windriver.com>
发送时间: 2021年1月26日 16:29
收件人: valentin.schneider@arm.com
抄送: peterz@infradead.org; linux-kernel@vger.kernel.org
主题: [PATCH] sched/core: add rcu_read_lock/unlock() protection

>From: Zqiang <qiang.zhang@windriver.com>

>Due to for_each_process_thread belongs to RCU read operation,
>need to add rcu_read_lock/unlock() protection.

  Sorry to disturb you
  I find it's already in the RCU critical zone
  Please ignore this change


>Signed-off-by: Zqiang <qiang.zhang@windriver.com>
>---
> kernel/sched/core.c | 2 ++
> 1 file changed, 2 insertions(+)
>
>diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>index 8c5481077c9c..c3f0103fdf53 100644
>--- a/kernel/sched/core.c
>+++ b/kernel/sched/core.c
>@@ -7738,6 +7738,7 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
>        lockdep_assert_held(&rq->lock);
>
>        printk("%sCPU%d enqueued tasks (%u total):\n", loglvl, cpu, rq->nr_running);
>+       rcu_read_lock();
>        for_each_process_thread(g, p) {
>                if (task_cpu(p) != cpu)
>                        continue;
>@@ -7747,6 +7748,7 @@ static void dump_rq_tasks(struct rq *rq, const char *loglvl)
>
>                printk("%s\tpid: %d, name: %s\n", loglvl, p->pid, p->comm);
>        }
>+       rcu_read_unlock();
> }
>
> int sched_cpu_dying(unsigned int cpu)
--
2.17.1