From a529e6f6579e30c3e9a18dc30a87a62be169acde Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Tue, 2 Jun 2009 08:09:17 -0400 Subject: ext4: fix bb_prealloc_list corruption due to wrong group locking (cherry-picked from commit d33a1976fbee1ee321d6f014333d8f03a39d526c) This is for Red Hat bug 490026: EXT4 panic, list corruption in ext4_mb_new_inode_pa ext4_lock_group(sb, group) is supposed to protect this list for each group, and a common code flow to remove an album is like this: ext4_get_group_no_and_offset(sb, pa->pa_pstart, &grp, NULL); ext4_lock_group(sb, grp); list_del(&pa->pa_group_list); ext4_unlock_group(sb, grp); so it's critical that we get the right group number back for this prealloc context, to lock the right group (the one associated with this pa) and prevent concurrent list manipulation. however, ext4_mb_put_pa() passes in (pa->pa_pstart - 1) with a comment, "-1 is to protect from crossing allocation group". This makes sense for the group_pa, where pa_pstart is advanced by the length which has been used (in ext4_mb_release_context()), and when the entire length has been used, pa_pstart has been advanced to the first block of the next group. However, for inode_pa, pa_pstart is never advanced; it's just set once to the first block in the group and not moved after that. So in this case, if we subtract one in ext4_mb_put_pa(), we are actually locking the *previous* group, and opening the race with the other threads which do not subtract off the extra block. Signed-off-by: Eric Sandeen Signed-off-by: "Theodore Ts'o" Signed-off-by: Greg Kroah-Hartman --- fs/ext4/mballoc.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'fs') diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index ceb68db799e..f34dadacbd9 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -3698,6 +3698,7 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *ac, struct super_block *sb, struct ext4_prealloc_space *pa) { unsigned long grp; + ext4_fsblk_t grp_blk; if (!atomic_dec_and_test(&pa->pa_count) || pa->pa_free != 0) return; @@ -3712,8 +3713,12 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *ac, pa->pa_deleted = 1; spin_unlock(&pa->pa_lock); - /* -1 is to protect from crossing allocation group */ - ext4_get_group_no_and_offset(sb, pa->pa_pstart - 1, &grp, NULL); + grp_blk = pa->pa_pstart; + /* If linear, pa_pstart may be in the next group when pa is used up */ + if (pa->pa_linear) + grp_blk--; + + ext4_get_group_no_and_offset(sb, grp_blk, &grp, NULL); /* * possible race: -- cgit v1.2.3-18-g5258