[PATCH 20/21] fat: ->i_pos race fix

OGAWA Hirofumi
2008-10-15T14:06:24Z

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@mail.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);
_