Re: [PATCH] ext4: deaccount delayed allocations at freeing inode in ext4_evict_inode()

[Konstantin Khlebnikov]

On 08/11/2019 05.08, Ritesh Harjani wrote:
> On 10/29/19 12:47 PM, Konstantin Khlebnikov wrote:
> > If inode->i_blocks is zero then ext4_evict_inode() skips ext4_truncate().
> > Delayed allocation extents are freed later in ext4_clear_inode() but this
> > happens when quota reference is already dropped. This leads to leak of
> > reserved space in quota block, which disappears after umount-mount.
> >
> > This seems broken for a long time but worked somehow until recent changes
> > in delayed allocation.
>
> Sorry, I may have missed it, but could you please help understand
> what recent changes in delayed allocation make this break or worse?

I don't see problem for 4.19. Haven't bisected yet.
Most likely this is around 'reserved cluster accounting'.

I suspect before these changes something always triggered da before unlink and
space usage committed and then truncated at eviction.

> A silly query, since I couldn't figure it out. Maybe the code has been
> there ever since like this:-

> So why can't we just move drop_dquot later after the ext4_es_remove_extent() (in function ext4_clear_inode)? Any known
> problems around that?

Clear_inode is called also when inode evicts from cache while it has nlinks
and stays at disk. I'm not sure how this must interact with reserves.

> -ritesh
>
>
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> > ---
> > Â fs/ext4/inode.c |ÂÂÂ 9 +++++++++
> > Â 1 file changed, 9 insertions(+)
> >
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 516faa280ced..580898145e8f 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -293,6 +293,15 @@ void ext4_evict_inode(struct inode *inode)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ inode->i_ino, err);
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ goto stop_handle;
> > ÂÂÂÂÂÂÂÂÂ }
> > +ÂÂÂ } else if (EXT4_I(inode)->i_reserved_data_blocks) {
> > +ÂÂÂÂÂÂÂ /* Deaccount reserve if inode has only delayed allocations. */
> > +ÂÂÂÂÂÂÂ err = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
> > +ÂÂÂÂÂÂÂ if (err) {
> > +ÂÂÂÂÂÂÂÂÂÂÂ ext4_warning(inode->i_sb,
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ "couldn't remove extents %lu (err %d)",
> > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ inode->i_ino, err);
> > +ÂÂÂÂÂÂÂÂÂÂÂ goto stop_handle;
> > +ÂÂÂÂÂÂÂ }
> > ÂÂÂÂÂ }
> >
> > ÂÂÂÂÂ /* Remove xattr references. */