linux-kernel - [PATCH 20/21] fat: ->i

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Date:	Wed, 15 Oct 2008 22:58:01 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, hirofumi@...l.parknet.co.jp
Subject: [PATCH 20/21] fat: ->i_pos race fix


i_pos is 64bits value, hence it's not atomic to update.

Important place is fat_write_inode() only, other places without lock
are just for printk().

This adds lock for "BITS_PER_LONG == 32" kernel.

Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
---

 fs/fat/inode.c |   21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff -puN fs/fat/inode.c~fat_i_pos-race-fix fs/fat/inode.c
--- linux-2.6/fs/fat/inode.c~fat_i_pos-race-fix	2008-09-29 19:04:03.000000000 +0900
+++ linux-2.6-hirofumi/fs/fat/inode.c	2008-09-29 19:04:03.000000000 +0900
@@ -542,6 +542,20 @@ static int fat_statfs(struct dentry *den
 	return 0;
 }
 
+static inline loff_t fat_i_pos_read(struct msdos_sb_info *sbi,
+				    struct inode *inode)
+{
+	loff_t i_pos;
+#if BITS_PER_LONG == 32
+	spin_lock(&sbi->inode_hash_lock);
+#endif
+	i_pos = MSDOS_I(inode)->i_pos;
+#if BITS_PER_LONG == 32
+	spin_unlock(&sbi->inode_hash_lock);
+#endif
+	return i_pos;
+}
+
 static int fat_write_inode(struct inode *inode, int wait)
 {
 	struct super_block *sb = inode->i_sb;
@@ -551,9 +565,12 @@ static int fat_write_inode(struct inode 
 	loff_t i_pos;
 	int err;
 
+	if (inode->i_ino == MSDOS_ROOT_INO)
+		return 0;
+
 retry:
-	i_pos = MSDOS_I(inode)->i_pos;
-	if (inode->i_ino == MSDOS_ROOT_INO || !i_pos)
+	i_pos = fat_i_pos_read(sbi, inode);
+	if (!i_pos)
 		return 0;
 
 	bh = sb_bread(sb, i_pos >> sbi->dir_per_block_bits);
_
--
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