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List:       xen-cvs
Subject:    [Xen-changelog] [linux-2.6.18-xen] blktap: fix race memory refernce
From:       "Xen patchbot-linux-2.6.18-xen"
Date:       2009-04-28 16:15:14
Message-ID: 200904281615.n3SGFFZO015128 () xenbits ! xensource ! com
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# HG changeset patch
# User Keir Fraser <keir.fraser@citrix.com>
# Date 1240922586 -3600
# Node ID 3232c6e19bdc219363446f837c4136dc9959c205
# Parent  613216635ff0d0adf114bd5106bb37ae74fff458
blktap: fix race memory refernce with ring_ok.

fix race memory refernce with ring_ok.
ring_ok is shared by mmapping process and blktap kernel thread.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
---
 drivers/xen/blktap/blktap.c |    5 +++++
 1 files changed, 5 insertions(+)

diff -r 613216635ff0 -r 3232c6e19bdc drivers/xen/blktap/blktap.c
--- a/drivers/xen/blktap/blktap.c	Tue Apr 28 13:42:32 2009 +0100
+++ b/drivers/xen/blktap/blktap.c	Tue Apr 28 13:43:06 2009 +0100
@@ -617,6 +617,9 @@ static int blktap_release(struct inode *
 	if (!info)
 		return 0;
 
+	info->ring_ok = 0;
+	smp_wmb();
+
 	info->dev_inuse = 0;
 	DPRINTK("Freeing device [/dev/xen/blktap%d]\n",info->minor);
 
@@ -717,6 +720,7 @@ static int blktap_mmap(struct file *filp
 #endif
 
 	info->vma = vma;
+	smp_wmb();
 	info->ring_ok = 1;
 	return 0;
  fail:
@@ -1390,6 +1394,7 @@ static void dispatch_rw_block_io(blkif_t
 		WPRINTK("blktap: ring not ready for requests!\n");
 		goto fail_response;
 	}
+	smp_rmb();
 
 	if (RING_FULL(&info->ufe_ring)) {
 		WPRINTK("blktap: fe_ring is full, can't add "

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