Messages in this thread | | | Date | Fri, 10 Jun 2022 08:45:42 +0530 | Subject | Re: [PATCH] rcu/tree: Add comment to describe GP done condition in fqs loop | From | Neeraj Upadhyay <> |
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On 6/10/2022 1:53 AM, Paul E. McKenney wrote: > On Thu, Jun 09, 2022 at 12:43:40PM +0530, Neeraj Upadhyay wrote: >> Add a comment to explain why !rcu_preempt_blocked_readers_cgp() condition >> is required on root rnp node, for GP completion check in rcu_gp_fqs_loop(). >> >> Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com> > > Thank you, Neeraj! As usual, I could not resist the urge to wordsmith > as shown below. Could you please check to see if I messed something up?
Thanks! > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit bdf3a744d3ad21336a390bfcc2e41de63f193eaf > Author: Neeraj Upadhyay <quic_neeraju@quicinc.com> > Date: Thu Jun 9 12:43:40 2022 +0530 > > rcu/tree: Add comment to describe GP-done condition in fqs loop > > Add a comment to explain why !rcu_preempt_blocked_readers_cgp() condition > is required on root rnp node, for GP completion check in rcu_gp_fqs_loop(). > > Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index a93c5f4d7e092..9a941e7ee6109 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2083,7 +2083,15 @@ static noinline_for_stack void rcu_gp_fqs_loop(void) > rcu_gp_torture_wait(); > WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS); > /* Locking provides needed memory barriers. */ > - /* If grace period done, leave loop. */ > + /* > + * Exit the loop if the root rcu_node structure indicates that the grace period > + * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check
We can remove ", leave the loop" ?
> + * is required only for single-node rcu_node trees because readers blocking > + * the current grace period are queued only on leaf rcu_node structures. > + * For multi-node trees, checking the root node's ->qsmask suffices, because a > + * given root node's ->qsmask bit is cleared only when all CPUs and tasks from
Do we need to say "a given root node's" , we have only single RCU node in the system, so we can just say, "because root node's ->qsmask bit is cleared..." ?
> + * the corresponding leaf node have passed through their quiescent state.
Change "the corresponding leaf node" to "their corresponding leaf nodes" or "the corresponding leaf nodes"?
Thanks Neeraj
> + */ > if (!READ_ONCE(rnp->qsmask) && > !rcu_preempt_blocked_readers_cgp(rnp)) > break;
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