From: Theodore Ts'o Subject: [PATCH FOR-STABLE-2.6.28 12/24] ext4: Fix race between read_block_bitmap() and mark_diskspace_used() Date: Tue, 17 Feb 2009 10:32:30 -0500 Message-ID: <1234884762-13580-13-git-send-email-tytso@mit.edu> References: <1234884762-13580-1-git-send-email-tytso@mit.edu> <1234884762-13580-2-git-send-email-tytso@mit.edu> <1234884762-13580-3-git-send-email-tytso@mit.edu> <1234884762-13580-4-git-send-email-tytso@mit.edu> <1234884762-13580-5-git-send-email-tytso@mit.edu> <1234884762-13580-6-git-send-email-tytso@mit.edu> <1234884762-13580-7-git-send-email-tytso@mit.edu> <1234884762-13580-8-git-send-email-tytso@mit.edu> <1234884762-13580-9-git-send-email-tytso@mit.edu> <1234884762-13580-10-git-send-email-tytso@mit.edu> <1234884762-13580-11-git-send-email-tytso@mit.edu> <1234884762-13580-12-git-send-email-tytso@mit.edu> Cc: linux-ext4@vger.kernel.org, "Aneesh Kumar K.V" , "Theodore Ts'o" To: stable@kernel.org Return-path: Received: from thunk.org ([69.25.196.29]:33239 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751767AbZBQQIr (ORCPT ); Tue, 17 Feb 2009 11:08:47 -0500 In-Reply-To: <1234884762-13580-12-git-send-email-tytso@mit.edu> Sender: linux-ext4-owner@vger.kernel.org List-ID: From: Aneesh Kumar K.V 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 (cherry picked from commit e8134b27e351e813414da3b95aa8eac6d3908088) --- fs/ext4/mballoc.c | 15 ++++++++++----- 1 files changed, 10 insertions(+), 5 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index d4283b4..dfcdda7 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++; } } @@ -3033,10 +3039,9 @@ 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);