Messages in this thread Patch in this message | | | Date | Mon, 22 Jun 2020 16:18:29 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu/tree: Remove CONFIG_PREMPT_RCU check in force_qs_rnp |
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On Mon, Jun 22, 2020 at 11:37:03PM +0530, Neeraj Upadhyay wrote: > Remove CONFIG_PREMPT_RCU check in force_qs_rnp(). Originally, > this check was required to skip executing fqs failsafe > for rcu-sched, which was added in commit a77da14ce9af ("rcu: > Yet another fix for preemption and CPU hotplug"). However, > this failsafe has been removed, since then. So, cleanup the > code to avoid any confusion around the need for boosting, > for !CONFIG_PREMPT_RCU. > > Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Good point, there is a !PREEMPT definition of the function rcu_preempt_blocked_readers_cgp() that unconditionally returns zero. And if !PREEMPT kernels, the same things happens in the "if" body as after it, so behavior is not changed.
I have queued and pushed this with an upgraded commit log as shown below.
Thanx, Paul
> --- > kernel/rcu/tree.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 6226bfb..57c904b 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2514,8 +2514,7 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) > raw_spin_lock_irqsave_rcu_node(rnp, flags); > rcu_state.cbovldnext |= !!rnp->cbovldmask; > if (rnp->qsmask == 0) { > - if (!IS_ENABLED(CONFIG_PREEMPT_RCU) || > - rcu_preempt_blocked_readers_cgp(rnp)) { > + if (rcu_preempt_blocked_readers_cgp(rnp)) { > /* > * No point in scanning bits because they > * are all zero. But we might need to > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project
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commit a4600389c35010aef414b89e2817d4a527e751b5 Author: Neeraj Upadhyay <neeraju@codeaurora.org> Date: Mon Jun 22 23:37:03 2020 +0530
rcu/tree: Remove CONFIG_PREMPT_RCU check in force_qs_rnp() Originally, the call to rcu_preempt_blocked_readers_cgp() from force_qs_rnp() had to be conditioned on CONFIG_PREEMPT_RCU=y, as in commit a77da14ce9af ("rcu: Yet another fix for preemption and CPU hotplug"). However, there is now a CONFIG_PREEMPT_RCU=n definition of rcu_preempt_blocked_readers_cgp() that unconditionally returns zero, so invoking it is now safe. In addition, the CONFIG_PREEMPT_RCU=n definition of rcu_initiate_boost() simply releases the rcu_node structure's ->lock, which is what happens when the "if" condition evaluates to false. This commit therefore drops the IS_ENABLED(CONFIG_PREEMPT_RCU) check, so that rcu_initiate_boost() is called only in CONFIG_PREEMPT_RCU=y kernels when there are readers blocking the current grace period. This does not change the behavior, but reduces code-reader confusion by eliminating non-CONFIG_PREEMPT_RCU=y calls to rcu_initiate_boost(). Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 6226bfb..57c904b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2514,8 +2514,7 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) raw_spin_lock_irqsave_rcu_node(rnp, flags); rcu_state.cbovldnext |= !!rnp->cbovldmask; if (rnp->qsmask == 0) { - if (!IS_ENABLED(CONFIG_PREEMPT_RCU) || - rcu_preempt_blocked_readers_cgp(rnp)) { + if (rcu_preempt_blocked_readers_cgp(rnp)) { /* * No point in scanning bits because they * are all zero. But we might need to
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