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Date: Tue, 24 Jan 2017 13:46:33 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH v3 tip/core/rcu 6/6] rcu: Adjust FQS offline checks for exact online-CPU detection Commit 7ec99de36f40 ("rcu: Provide exact CPU-online tracking for RCU"), as its title suggests, got rid of RCU's remaining CPU-hotplug timing guesswork. This commit therefore removes the one-jiffy kludge that was used to paper over this guesswork. Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@...htriplett.org> --- kernel/rcu/tree.c | 17 ++--------------- 1 file changed, 2 insertions(+), 15 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index d8245cbd08f9..6e4b1dcebeb2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1276,21 +1276,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, return 1; } - /* - * Check for the CPU being offline, but only if the grace period - * is old enough. We don't need to worry about the CPU changing - * state: If we see it offline even once, it has been through a - * quiescent state. - * - * The reason for insisting that the grace period be at least - * one jiffy old is that CPUs that are not quite online and that - * have just gone offline can still execute RCU read-side critical - * sections. - */ - if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies)) - return 0; /* Grace period is not old enough. */ - barrier(); - if (cpu_is_offline(rdp->cpu)) { + /* Check for the CPU being offline. */ + if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl")); rdp->offline_fqs++; return 1; -- 2.5.2
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