Messages in this thread | | | Subject | Re: [PATCH] rcu/tree: Remove CONFIG_PREMPT_RCU check in force_qs_rnp | From | Neeraj Upadhyay <> | Date | Tue, 23 Jun 2020 11:51:47 +0530 |
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Hi Paul,
On 6/23/2020 4:48 AM, Paul E. McKenney wrote: > 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 >
Thanks! patch looks good to me!
Thanks Neeraj
>> --- >> 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 > > ------------------------------------------------------------------------ > > 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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