On Mon, Mar 03, 2014 at 03:00:28PM +0100, Maurizio Lombardi wrote:
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 08ddfda..546575a 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3059,6 +3059,21 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
> size = ac->ac_o_ex.fe_len << bsbits;
> }
> size = size >> bsbits;
> +
> + /* In any case, the size cannot be greater than the number
> + * of maximum free blocks per group.
> + */
> + if (size > EXT4_BLOCKS_PER_GROUP(ac->ac_sb)) {
> + int sz_log2;
> +
> + size = EXT4_BLOCKS_PER_GROUP(ac->ac_sb);
> +
> + /* Recalculate the start offset */
> + sz_log2 = __fls(size << bsbits);
> + start_off = ((loff_t) ac->ac_o_ex.fe_logical >>
> + (sz_log2 - bsbits)) << sz_log2;
> + }
> +
> start = start_off >> bsbits;
>
> /* don't cover already allocated blocks in selected range */
This definitely fixes the bug. However, there will be some cases
where if the blocks per group is sufficiently small, where for smaller
files, start_off would have been 0 instead of that complicated
expression.
Looking at ext4_mb_normalize_request(), exactly what this code is
trying to do is actually a bit opaque to me, and every time I look at
it I get a headache.
Andreas, can you take a look at this? I think you may know this code
better --- and it's somewhere I've been waiting to do some cleanup, or
at least some improved code comments.
Thanks!!
- Ted
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