From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Subject: kernel/hung_task.c: break RCU locks based on jiffies check_hung_uninterruptible_tasks() is currently calling rcu_lock_break() for every 1024 threads. But check_hung_task() is very slow if printk() was called, and is very fast otherwise. If many threads within some 1024 threads called printk(), the RCU grace period might be extended enough to trigger RCU stall warnings. Therefore, calling rcu_lock_break() for every some fixed jiffies will be safer. Link: http://lkml.kernel.org/r/1544800658-11423-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> Cc: Petr Mladek <pmladek@xxxxxxxx> Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- kernel/hung_task.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/kernel/hung_task.c~kernel-hung_taskc-break-rcu-locks-based-on-jiffies +++ a/kernel/hung_task.c @@ -34,7 +34,7 @@ int __read_mostly sysctl_hung_task_check * is disabled during the critical section. It also controls the size of * the RCU grace period. So it needs to be upper-bound. */ -#define HUNG_TASK_BATCHING 1024 +#define HUNG_TASK_LOCK_BREAK (HZ / 10) /* * Zero means infinite timeout - no checking done: @@ -171,7 +171,7 @@ static bool rcu_lock_break(struct task_s static void check_hung_uninterruptible_tasks(unsigned long timeout) { int max_count = sysctl_hung_task_check_count; - int batch_count = HUNG_TASK_BATCHING; + unsigned long last_break = jiffies; struct task_struct *g, *t; /* @@ -186,10 +186,10 @@ static void check_hung_uninterruptible_t for_each_process_thread(g, t) { if (!max_count--) goto unlock; - if (!--batch_count) { - batch_count = HUNG_TASK_BATCHING; + if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) { if (!rcu_lock_break(g, t)) goto unlock; + last_break = jiffies; } /* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */ if (t->state == TASK_UNINTERRUPTIBLE) _
