linux-ext4 - Re: [PATCH] Free allocated and pre-allocated blocks when check_eofblocks

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Date:	Tue, 21 Jun 2011 12:40:04 -0700
From:	Jiaying Zhang <jiayingz@...gle.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Theodore Tso <tytso@....edu>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] Free allocated and pre-allocated blocks when
 check_eofblocks_fl fails

On Tue, Jun 21, 2011 at 8:24 AM, Lukas Czerner <lczerner@...hat.com> wrote:
>
> On Mon, 20 Jun 2011, Jiaying Zhang wrote:
>
> > We have hit the same BUG_ON as described in
> > https://bugzilla.kernel.org/show_bug.cgi?id=31222
> > on some of our servers that have disk failures or corrupted inodes. After
> > looking at the code, I think the problem is that we are not freeing inode's
> > preallocation list when check_eofblocks_fl fails in ext4_ext_map_blocks(),
> > which leaves the inode's preallocation list in an inconsistent state.
> >
> > Below is a proposed patch to fix the bug. I have tested it by manually
> > inserting a random failure in check_eofblocks_fl() and run a test that
> > creates and uses an inode's preallocated blocks. Without the fix, the kernel
> > crashes after a few runs. With the fix, no crash is observed.
> >
> > ext4: free allocated and pre-allocated blocks when check_eofblocks_fl fails
> >
> > Upon corrupted inode or disk failures, we may fail after we already allocate
> > some blocks from the inode or take some blocks from the inode's preallocation
> > list, but before we successfully insert the corresponding extent to the extent
> > tree. In this case, we should free any allocated blocks and discard the inode's
> > preallocated blocks because the entries in the inode's preallocation list may
> > be in an inconsistent state.
> >
> > Signed-off-by: Jiaying Zhang <jiayingz@...gle.com>
>
> Hi,
>
> the change looks good to me (with one note), but the patch itself is not very
> well formated, and Ted would have to copy it out. Please use this:
>
> ext4: free allocated and pre-allocated blocks when check_eofblocks_fl fails
>
> for Subject line and put any comments which should not appear in the
> commit description after signed-off-by line starting with "--- " line.
> Or just use git format-patch.
Thanks for the suggestion. I will re-send the patch with correct format.

>
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 5199bac..8cf6ec9 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -3596,10 +3596,8 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
> >       }
> >
> >       err = check_eofblocks_fl(handle, inode, map->m_lblk, path, ar.len);
> > -     if (err)
> > -             goto out2;
> > -
> > -     err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
> > +     if (!err)
> > +             err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
> >       if (err) {
>
> why not to use:
>        else {
>
It is not the same. If there is an error from ext4_ext_insert_extent(),
we also want to free allocated blocks.

Jiaying
>
> >               /* free data blocks we just allocated */
> >               /* not a good idea to call discard here directly,
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
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> >
>
> Thanks!
> -Lukas
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