From 011cad0bf33dc86ce40fe18557b19a42fbc4e657 Mon Sep 17 00:00:00 2001 Message-Id: <011cad0bf33dc86ce40fe18557b19a42fbc4e657.1522097754.git.Jim.Somerville@windriver.com> In-Reply-To: References: From: "Paul E. McKenney" Date: Thu, 15 Dec 2016 15:37:47 -0800 Subject: [PATCH 16/27] rcu: Don't wake rcuc/X kthreads on NOCB CPUs [ upstream 630c7ed9ca0608912fa7c8591d05dfc8742dc9e6 in tip repo ] Chris Friesen notice that rcuc/X kthreads were consuming CPU even on NOCB CPUs. This makes no sense because the only purpose or these kthreads is to invoke normal (non-offloaded) callbacks, of which there will never be any on NOCB CPUs. This problem was due to a bug in cpu_has_callbacks_ready_to_invoke(), which should have been checking ->nxttail[RCU_NEXT_TAIL] for NULL, but which was instead (incorrectly) checking ->nxttail[RCU_DONE_TAIL]. Because ->nxttail[RCU_DONE_TAIL] is never NULL, the only effect is to cause the rcuc/X kthread to execute when it should not do so. This commit therefore checks ->nxttail[RCU_NEXT_TAIL], which is NULL for NOCB CPUs. Reported-by: Chris Friesen Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett Signed-off-by: Jim Somerville --- kernel/rcutree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index f46e3e4..ac3dfb7 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -300,7 +300,7 @@ static int cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) { return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] && - rdp->nxttail[RCU_DONE_TAIL] != NULL; + rdp->nxttail[RCU_NEXT_TAIL] != NULL; } /* -- 1.8.3.1