From: Aneesh Kumar K.V Date: Tue, 6 Jan 2009 02:38:26 +0000 (-0500) Subject: ext4: Fix race between read_block_bitmap() and mark_diskspace_used() X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=e8134b27e351e813414da3b95aa8eac6d3908088;p=linux-2.6-omap-h63xx.git ext4: Fix race between read_block_bitmap() and mark_diskspace_used() We need to make sure we update the block bitmap and clear EXT4_BG_BLOCK_UNINIT flag with sb_bgl_lock held, since ext4_read_block_bitmap() looks at EXT4_BG_BLOCK_UNINIT to decide whether to initialize the block bitmap each time it is called (introduced by commit c806e68f), and this can race with block allocations in ext4_mb_mark_diskspace_used(). ext4_read_block_bitmap does: spin_lock(sb_bgl_lock(EXT4_SB(sb), block_group)); if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) { ext4_init_block_bitmap(sb, bh, block_group, desc); Now on the block allocation side we do mb_set_bits(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group), bitmap_bh->b_data, ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len); .... spin_lock(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group)); if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) { gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT); ie on allocation we update the bitmap then we take the sb_bgl_lock and clear the EXT4_BG_BLOCK_UNINIT flag. What can happen is a parallel ext4_read_block_bitmap can zero out the bitmap in between the above mb_set_bits and spin_lock(sb_bg_lock..) The race results in below user visible errors EXT4-fs error (device sdb1): ext4_mb_release_inode_pa: free 100, pa_free 105 EXT4-fs error (device sdb1): mb_free_blocks: double-free of inode 0's block .. Signed-off-by: Aneesh Kumar K.V Signed-off-by: "Theodore Ts'o" Cc: stable@kernel.org --- diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index cda69632eea..d559a03f3eb 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -1070,7 +1070,10 @@ static void mb_clear_bits(spinlock_t *lock, void *bm, int cur, int len) cur += 32; continue; } - mb_clear_bit_atomic(lock, cur, bm); + if (lock) + mb_clear_bit_atomic(lock, cur, bm); + else + mb_clear_bit(cur, bm); cur++; } } @@ -1088,7 +1091,10 @@ static void mb_set_bits(spinlock_t *lock, void *bm, int cur, int len) cur += 32; continue; } - mb_set_bit_atomic(lock, cur, bm); + if (lock) + mb_set_bit_atomic(lock, cur, bm); + else + mb_set_bit(cur, bm); cur++; } } @@ -3035,10 +3041,9 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac, } } #endif - mb_set_bits(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group), bitmap_bh->b_data, - ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len); - spin_lock(sb_bgl_lock(sbi, ac->ac_b_ex.fe_group)); + mb_set_bits(NULL, bitmap_bh->b_data, + ac->ac_b_ex.fe_start, ac->ac_b_ex.fe_len); if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) { gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT); gdp->bg_free_blocks_count =