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rcu: Motivate Tiny RCU forward progress 

If a long-running CPU-bound in-kernel task invokes call_rcu(), the
callback won't be invoked until the next context switch.  If there are
no other runnable tasks (which is not an uncommon situation on deep
embedded systems), the callback might never be invoked.

This commit therefore causes rcu_check_callbacks() to ask the scheduler
for a context switch if there are callbacks posted that are still waiting
for a grace period.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-07-20 14:18:23 -07:00
parent c116dba68d
commit c5bacd9417
1 changed files with 5 additions and 1 deletions
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6
kernel/rcu/tiny.c
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@ -78,8 +78,12 @@ void rcu_qs(void)
*/
void rcu_check_callbacks(int user)
{
if (user)
if (user) {
rcu_qs();
} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
set_tsk_need_resched(current);
set_preempt_need_resched();
}
}
/* Invoke the RCU callbacks whose grace period has elapsed. */