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rcu/nocb: Never downgrade ->nocb_defer_wakeup in wake_nocb_gp_defer()

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Currently, wake_nocb_gp_defer() simply stores whatever waketype was
passed in, which can result in a RCU_NOCB_WAKE_FORCE being downgraded
to RCU_NOCB_WAKE, which could in turn delay callback processing.
This commit therefore adds a check so that wake_nocb_gp_defer() only
updates ->nocb_defer_wakeup when the update increases the forcefulness,
thus avoiding downgrades.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
This commit is contained in:
Paul E. McKenney 2019-05-23 13:49:26 -07:00
parent aeeacd9d84
commit 383e133283
1 changed files with 2 additions and 1 deletions
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3
kernel/rcu/tree_plugin.h
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@ -1600,7 +1600,8 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
{
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
mod_timer(&rdp->nocb_timer, jiffies + 1);
WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
if (rdp->nocb_defer_wakeup < waketype)
WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
}