From 98283bb49c6c8c070ebde9f47489d3e9a83c1323 Mon Sep 17 00:00:00 2001 From: OGAWA Hirofumi Date: Mon, 16 Jul 2007 09:40:05 +0900 Subject: [PATCH] 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 Signed-off-by: Linus Torvalds --- fs/fat/fatent.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c index ab171ea8e86..2c1b73fb82a 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) -- 2.20.1