From: OGAWA Hirofumi Date: Mon, 16 Jul 2007 00:40:05 +0000 (+0900) Subject: fat: Fix the race of read/write the FAT12 entry X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=98283bb49c6c8c070ebde9f47489d3e9a83c1323;p=linux-beck.git 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 --- 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)