linux-kernel - [PATCH 08/10] edac_core: Uses call_rcu() and its own wait_for

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Message-ID: <20090623150434.22490.18824.stgit@localhost>
Date:	Tue, 23 Jun 2009 17:04:34 +0200
From:	Jesper Dangaard Brouer <hawk@...x.dk>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	Jesper Dangaard Brouer <hawk@...x.dk>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	dougthompson@...ssion.com, bluesmoke-devel@...ts.sourceforge.net,
	axboe@...nel.dk, "Patrick McHardy" <kaber@...sh.net>,
	christine.caulfield@...glemail.com, Trond.Myklebust@...app.com,
	linux-wireless@...r.kernel.org, johannes@...solutions.net,
	yoshfuji@...ux-ipv6.org, shemminger@...ux-foundation.org,
	linux-nfs@...r.kernel.org, bfields@...ldses.org, neilb@...e.de,
	linux-ext4@...r.kernel.org, tytso@....edu, adilger@....com,
	netfilter-devel@...r.kernel.org
Subject: [PATCH 08/10] edac_core: Uses call_rcu() and its own
	wait_for_completion scheme.

Module edac_core.ko uses call_rcu() callbacks in edac_device.c, edac_mc.c
and edac_pci.c.

They all uses a wait_for_completion scheme, but this scheme it not 100%
safe on multiple CPUs.  See the _rcu_barrier() implementation which explains
why extra precausion is needed.

The patch adds a comment about rcu_barrier() and as a precausion calls
rcu_barrier().  A maintainer needs to look at removing the wait_for_completion
code.

Signed-off-by: Jesper Dangaard Brouer <hawk@...x.dk>
---

 drivers/edac/edac_device.c |    5 +++++
 drivers/edac/edac_mc.c     |    5 +++++
 drivers/edac/edac_pci.c    |    5 +++++
 3 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/drivers/edac/edac_device.c b/drivers/edac/edac_device.c
index b02a6a6..5e831c9 100644
--- a/drivers/edac/edac_device.c
+++ b/drivers/edac/edac_device.c
@@ -373,6 +373,11 @@ static void del_edac_device_from_global_list(struct edac_device_ctl_info
 	init_completion(&edac_device->removal_complete);
 	call_rcu(&edac_device->rcu, complete_edac_device_list_del);
 	wait_for_completion(&edac_device->removal_complete);
+
+	/* hawk@...x.dk 2009-06-22: I think that rcu_barrier() should
+	 *  be used instead of wait_for_completion, because
+	 *  rcu_barrier() take multiple CPUs into account */
+	rcu_barrier();
 }
 
 /*
diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
index 335b7eb..edcce41 100644
--- a/drivers/edac/edac_mc.c
+++ b/drivers/edac/edac_mc.c
@@ -428,6 +428,11 @@ static void del_mc_from_global_list(struct mem_ctl_info *mci)
 	init_completion(&mci->complete);
 	call_rcu(&mci->rcu, complete_mc_list_del);
 	wait_for_completion(&mci->complete);
+
+	/* hawk@...x.dk 2009-06-22: I think that rcu_barrier() should
+	 *  be used instead of wait_for_completion, because
+	 *  rcu_barrier() take multiple CPUs into account */
+	rcu_barrier();
 }
 
 /**
diff --git a/drivers/edac/edac_pci.c b/drivers/edac/edac_pci.c
index 30b585b..d0eb8c9 100644
--- a/drivers/edac/edac_pci.c
+++ b/drivers/edac/edac_pci.c
@@ -188,6 +188,11 @@ static void del_edac_pci_from_global_list(struct edac_pci_ctl_info *pci)
 	init_completion(&pci->complete);
 	call_rcu(&pci->rcu, complete_edac_pci_list_del);
 	wait_for_completion(&pci->complete);
+
+	/* hawk@...x.dk 2009-06-22: I think that rcu_barrier() should
+	 *  be used instead of wait_for_completion, because
+	 *  rcu_barrier() take multiple CPUs into account */
+	rcu_barrier();
 }
 
 #if 0

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