48 lines
1.9 KiB
Diff
48 lines
1.9 KiB
Diff
From b48c1062db1a4529f9ebecbffb5a80542da9f4f5 Mon Sep 17 00:00:00 2001
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Message-Id: <b48c1062db1a4529f9ebecbffb5a80542da9f4f5.1528226387.git.Jim.Somerville@windriver.com>
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In-Reply-To: <c8270e79f6b7008fde44b8d5aa6314d8cf89d3ed.1528226387.git.Jim.Somerville@windriver.com>
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References: <c8270e79f6b7008fde44b8d5aa6314d8cf89d3ed.1528226387.git.Jim.Somerville@windriver.com>
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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
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Date: Thu, 15 Dec 2016 15:37:47 -0800
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Subject: [PATCH 18/32] rcu: Don't wake rcuc/X kthreads on NOCB CPUs
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[ upstream 630c7ed9ca0608912fa7c8591d05dfc8742dc9e6 in tip repo ]
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Chris Friesen notice that rcuc/X kthreads were consuming CPU even on
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NOCB CPUs. This makes no sense because the only purpose or these
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kthreads is to invoke normal (non-offloaded) callbacks, of which there
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will never be any on NOCB CPUs. This problem was due to a bug in
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cpu_has_callbacks_ready_to_invoke(), which should have been checking
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->nxttail[RCU_NEXT_TAIL] for NULL, but which was instead (incorrectly)
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checking ->nxttail[RCU_DONE_TAIL]. Because ->nxttail[RCU_DONE_TAIL] is
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never NULL, the only effect is to cause the rcuc/X kthread to execute
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when it should not do so.
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This commit therefore checks ->nxttail[RCU_NEXT_TAIL], which is NULL
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for NOCB CPUs.
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Reported-by: Chris Friesen <chris.friesen@windriver.com>
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Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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Signed-off-by: Jim Somerville <Jim.Somerville@windriver.com>
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---
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kernel/rcutree.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/kernel/rcutree.c b/kernel/rcutree.c
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index 9648918..fb7b2a8 100644
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--- a/kernel/rcutree.c
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+++ b/kernel/rcutree.c
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@@ -367,7 +367,7 @@ static int
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cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
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{
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return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
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- rdp->nxttail[RCU_DONE_TAIL] != NULL;
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+ rdp->nxttail[RCU_NEXT_TAIL] != NULL;
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}
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/*
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--
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1.8.3.1
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