From: Paul E. McKenney Date: Thu, 23 May 2019 20:49:26 +0000 (-0700) Subject: rcu/nocb: Never downgrade ->nocb_defer_wakeup in wake_nocb_gp_defer() X-Git-Tag: for-5.4/post-2019-09-24~45^2~1^2^2~18 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=383e13328373ae1e17119ff89c86ff5f9413f31c;p=linux-2.6-block.git rcu/nocb: Never downgrade ->nocb_defer_wakeup in wake_nocb_gp_defer() 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 --- diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 7077ef7bea96..b9e00660af60 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -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); }