linux-ext4 - [PATCH 01/10] ext4: Use rcu_barrier() on module unload.

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Date:	Tue, 23 Jun 2009 17:03:59 +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 01/10] ext4: Use rcu_barrier() on module unload.

The ext4 module uses rcu_call() thus it should use rcu_barrier()on
module unload.

The kmem cache ext4_pspace_cachep is sometimes free'ed using
call_rcu() callbacks.  Thus, we must wait for completion of call_rcu()
before doing kmem_cache_destroy().

I have difficult determining if no new call_rcu() callbacks can be envoked.
Would the maintainer please verify this?

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

 fs/ext4/mballoc.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 519a0a6..e271a9e 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2902,8 +2902,10 @@ int __init init_ext4_mballoc(void)
 
 void exit_ext4_mballoc(void)
 {
-	/* XXX: synchronize_rcu(); */
+	/* Wait for completion of call_rcu()'s on ext4_pspace_cachep */
+	rcu_barrier();
 	kmem_cache_destroy(ext4_pspace_cachep);
+
 	kmem_cache_destroy(ext4_ac_cachep);
 	kmem_cache_destroy(ext4_free_ext_cachep);
 }

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