Hello Josef,
> A user sent me a btrfs-image of a file system that was panicing on mount
> during
> the log recovery. I had originally thought these problems were from a bug in
> the free space cache code, but that was just a symptom of the problem. The
> problem is if your application does something like this
>
> [prealloc][prealloc][prealloc]
>
> the internal extent maps will merge those all together into one extent map,
> even
> though on disk they are 3 separate extents. So if you go to write into one of
> these ranges the extent map will be right since we use the physical extent
> when
> doing the write, but when we log the extents they will use the wrong sizes for
> the remainder prealloc space. If this doesn't happen to trip up the free
> space
> cache (which it won't in a lot of cases) then you will get bogus entries in
> your
> extent tree which will screw stuff up later. The data and such will still
> work,
> but everything else is broken. This patch fixes this by not allowing extents
> that are on the modified list to be merged. This has the side effect that we
> are no longer adding everything to the modified list all the time, which means
> we now have to call btrfs_drop_extents every time we log an extent into the
> tree. So this allows me to drop all this speciality code I was using to get
> around calling btrfs_drop_extents. With this patch the testcase I've created
> no
> longer creates a bogus file system after replaying the log. Thanks,
>
> Signed-off-by: Josef Bacik <jba...@fusionio.com>
>
<snip>
> while (1) {
> write_lock(&em_tree->lock);
> - err = add_extent_mapping(em_tree, hole_em);
> - if (!err)
> - list_move(&hole_em->list,
> - &em_tree->modified_extents);
> + err = add_extent_mapping(em_tree, hole_em, 1);
> write_unlock(&em_tree->lock);
> if (err != -EEXIST)
> break;
> @@ -5989,7 +5977,8 @@ static int merge_extent_mapping(struct extent_map_tree
> *em_tree,
> em->block_start += start_diff;
> em->block_len -= start_diff;
> }
> - return add_extent_mapping(em_tree, em);
> + printk(KERN_ERR "merging here for %Lu\n", em->orig_start);
How about using something like pr_debug here.
When i tested btrfs-next, i found it hit too much.
Thanks,
Wang
> + return add_extent_mapping(em_tree, em, 0);
> }
>
> static noinline int uncompress_inline(struct btrfs_path *path,
> @@ -6283,7 +6272,7 @@ insert:
>
> err = 0;
> write_lock(&em_tree->lock);
> - ret = add_extent_mapping(em_tree, em);
> + ret = add_extent_mapping(em_tree, em, 0);
> /* it is possible that someone inserted the extent into the tree
> * while we had the lock dropped. It is also possible that
> * an overlapping map exists in the tree
> @@ -6706,10 +6695,7 @@ static struct extent_map *create_pinned_em(struct
> inode *inode, u64 start,
> btrfs_drop_extent_cache(inode, em->start,
> em->start + em->len - 1, 0);
> write_lock(&em_tree->lock);
> - ret = add_extent_mapping(em_tree, em);
> - if (!ret)
> - list_move(&em->list,
> - &em_tree->modified_extents);
> + ret = add_extent_mapping(em_tree, em, 1);
> write_unlock(&em_tree->lock);
> } while (ret == -EEXIST);
<snip>
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