Messages in this thread Patch in this message | | | Date | Fri, 10 Jun 2022 10:00:18 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcu/tree: Add comment to describe GP done condition in fqs loop |
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On Fri, Jun 10, 2022 at 04:37:39PM +0000, Joel Fernandes 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> > > --- > > kernel/rcu/tree.c | 12 +++++++++++- > > 1 file changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index a93c5f4d7e09..9cd1ba512fdc 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -2083,7 +2083,17 @@ 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. */ > > + /* > > + * If grace period done, leave loop. rcu_preempt_blocked_readers_cgp(rnp) > > + * check is required for the case where we only have single node in the > > + * rcu_node tree; so, root rcu node is also the leaf node, where readers > > + * blocking current gp are queued. For multi-node tree, checking ->qsmask > > + * on the root node is sufficient, as root rcu node's ->qsmask is only > > + * cleared, when all leaf rcu nodes have propagated their quiescent > > + * state to their parent node, which happens only after both ->qsmask > > + * and rcu_preempt_blocked_readers_cgp(rnp_leaf) are cleared for those > > + * leaf nodes. > > + */ > > if (!READ_ONCE(rnp->qsmask) && > > !rcu_preempt_blocked_readers_cgp(rnp)) > > break; > > Paul's wording changes are OK with me. > > For the patch: > Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Applied, thank you!
Thanx, Paul
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