Hi all:
I'm looking in ext4_mb_use_preallocated() and am seeing something odd.
First we look through the inode prealloc list, and see if we have a
preallocation that satisfies the allocation context:
/* all fields in this condition don't change,
* so we can skip locking for them */
if (ac->ac_o_ex.fe_logical < pa->pa_lstart ||
ac->ac_o_ex.fe_logical >= pa->pa_lstart + pa->pa_len)
continue;
/* non-extent files can't have physical blocks past 2^32 */
if (!(EXT4_I(ac->ac_inode)->i_flags & EXT4_EXTENTS_FL) &&
pa->pa_pstart + pa->pa_len > EXT4_MAX_BLOCK_FILE_PHYS)
continue;
/* found preallocated blocks, use them */
spin_lock(&pa->pa_lock);
if (pa->pa_deleted == 0 && pa->pa_free) {
=> Now we're good, and have an AC that satisfies us.
=> We call ext4_mb_use_inode_pa(ac, pa);
But ext4_mb_use_inode_pa() has this:
BUG_ON(pa->pa_free < len);
Nowhere do we check the 'pa_free' value to decide if this preallocation is
okay to use.
Further down in ext4_mb_use_preallocated() we check the locality group
prealloc list; for this, we DO check pa_free:
spin_lock(&pa->pa_lock);
if (pa->pa_deleted == 0 &&
pa->pa_free >= ac->ac_o_ex.fe_len) {
cpa = ext4_mb_check_group_pa(goal_block,
pa, cpa);
So my question is: Is it a bug that we don't check that an inode
preallocation has enough free blocks for the AC before we try to use it? I
have hit the BUG_ON above at least once in my testing, but I can't
characterize what the workload was at the time (nor can I reproduce it...).
Thanks,
Curt
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
