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

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Date:	Wed, 22 Jun 2011 11:08:43 +0200 (CEST)
From:	Lukas Czerner <lczerner@...hat.com>
To:	Jiaying Zhang <jiayingz@...gle.com>
cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH RESEND] Free allocated and pre-allocated blocks when
 check_eofblocks_fl fails

On Tue, 21 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.
>     

Hi, have you even read my previous reply ?

> ext4: free allocated and pre-allocated blocks when check_eofblocks_fl fails

Why not to use this ^^^^^^^ line for a subject ? It is immediately
clear what filesystem is it for. Also, why do you have this line in the
commit description anyway ?

It seems that you intended to have the first two paragraphs just as
comments, but you do not really want it to be in commit description, is
that right ? So either add it into commit description or put it after
the "--- " line.

Thanks!
-Lukas

> 
> 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>
> ---
>  fs/ext4/extents.c |    6 ++----
>  1 files changed, 2 insertions(+), 4 deletions(-)
> 
> 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) {
>                 /* free data blocks we just allocated */
>                 /* not a good idea to call discard here directly,
> 

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