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authorOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>2007-07-16 09:40:05 +0900
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-16 10:31:01 -0700
commit98283bb49c6c8c070ebde9f47489d3e9a83c1323 (patch)
treef124325ac1768bee61b82e7689bc48ea102efe56
parent347e03df1696ab22963f6b8c4f2220c41ec17f82 (diff)
fat: Fix the race of read/write the FAT12 entry
FAT12 entry is 12bits, so it needs 2 phase to update the value. And writer and reader access it without any lock, so reader can get the half updated value. This fixes the long standing race condition by adding a global spinlock to only FAT12 for avoiding any impact against FAT16/32. Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/fat/fatent.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index ab171ea8e869..2c1b73fb82ae 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -17,6 +17,8 @@ struct fatent_operations {
int (*ent_next)(struct fat_entry *);
};
+static DEFINE_SPINLOCK(fat12_entry_lock);
+
static void fat12_ent_blocknr(struct super_block *sb, int entry,
int *offset, sector_t *blocknr)
{
@@ -116,10 +118,13 @@ static int fat12_ent_get(struct fat_entry *fatent)
u8 **ent12_p = fatent->u.ent12_p;
int next;
+ spin_lock(&fat12_entry_lock);
if (fatent->entry & 1)
next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
else
next = (*ent12_p[1] << 8) | *ent12_p[0];
+ spin_unlock(&fat12_entry_lock);
+
next &= 0x0fff;
if (next >= BAD_FAT12)
next = FAT_ENT_EOF;
@@ -151,6 +156,7 @@ static void fat12_ent_put(struct fat_entry *fatent, int new)
if (new == FAT_ENT_EOF)
new = EOF_FAT12;
+ spin_lock(&fat12_entry_lock);
if (fatent->entry & 1) {
*ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
*ent12_p[1] = new >> 4;
@@ -158,6 +164,7 @@ static void fat12_ent_put(struct fat_entry *fatent, int new)
*ent12_p[0] = new & 0xff;
*ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
}
+ spin_unlock(&fat12_entry_lock);
mark_buffer_dirty(fatent->bhs[0]);
if (fatent->nr_bhs == 2)