Re: [PATCH 4.9 083/116] btrfs: free block groups after freeing fs trees

[Sasha Levin]

On Thu, Feb 13, 2020 at 09:55:33PM +0100, David Sterba wrote:
> On Thu, Feb 13, 2020 at 07:20:27AM -0800, Greg Kroah-Hartman wrote:
> > From: Josef Bacik <josef@xxxxxxxxxxxxxx>
> >
> > [ Upstream commit 4e19443da1941050b346f8fc4c368aa68413bc88 ]
> >
> > Sometimes when running generic/475 we would trip the
> > WARN_ON(cache->reserved) check when free'ing the block groups on umount.
> > This is because sometimes we don't commit the transaction because of IO
> > errors and thus do not cleanup the tree logs until at umount time.
> >
> > These blocks are still reserved until they are cleaned up, but they
> > aren't cleaned up until _after_ we do the free block groups work.  Fix
> > this by moving the free after free'ing the fs roots, that way all of the
> > tree logs are cleaned up and we have a properly cleaned fs.  A bunch of
> > loops of generic/475 confirmed this fixes the problem.
> >
> > CC: stable@xxxxxxxxxxxxxxx # 4.9+
> > Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > Reviewed-by: David Sterba <dsterba@xxxxxxxx>
> > Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > ---
> >  fs/btrfs/disk-io.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index eab5a9065f093..439b5f5dc3274 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -3864,6 +3864,15 @@ void close_ctree(struct btrfs_root *root)
> >  	clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
> >  	free_root_pointers(fs_info, true);
> >
> > +	/*
> > +	 * We must free the block groups after dropping the fs_roots as we could
> > +	 * have had an IO error and have left over tree log blocks that aren't
> > +	 * cleaned up until the fs roots are freed.  This makes the block group
> > +	 * accounting appear to be wrong because there's pending reserved bytes,
> > +	 * so make sure we do the block group cleanup afterwards.
> > +	 */
> > +	btrfs_free_block_groups(fs_info);
>
> Something's wrong here.  The patch 4e19443da1 moves the
> btrfs_free_block_groups() call and the stable backport lacks the "-"
> line. However the patch applies cleanly on 4.9.213.
>
> 3855         btrfs_free_block_groups(fs_info);
> ^^^^
>
> 3856
> 3857         /*
> 3858          * we must make sure there is not any read request to
> 3859          * submit after we stopping all workers.
> 3860          */
> 3861         invalidate_inode_pages2(fs_info->btree_inode->i_mapping);
> 3862         btrfs_stop_all_workers(fs_info);
> 3863
> 3864         clear_bit(BTRFS_FS_OPEN, &fs_info->flags);
> 3865         free_root_pointers(fs_info, 1);
> 3866
> 3867         /*
> 3868          * We must free the block groups after dropping the fs_roots as we could
> 3869          * have had an IO error and have left over tree log blocks that aren't
> 3870          * cleaned up until the fs roots are freed.  This makes the block group
> 3871          * accounting appear to be wrong because there's pending reserved bytes,
> 3872          * so make sure we do the block group cleanup afterwards.
> 3873          */
> 3874         btrfs_free_block_groups(fs_info);
>
> The first one should not be there.

Sigh, sorry about that. The story behind this is that for this patch to
apply, we first must have 5cdd7db6c5c9 ("Btrfs: fix assertion failure
when freeing block groups at close_ctree()") which moves the
btrfs_free_block_groups() call to line 3863 in your code above.

I somehow goofed up picking it up and (probably) messed up the rebase
when it went missing, sorry again.

I'll fix it up for the next release.

--
Thanks,
Sasha