linux-ext4 - Re: [PATCH 1/3] ext4: Verify block bitmap even after fresh initialization

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Date:	Tue, 2 Jun 2015 09:59:32 +0200 (CEST)
From:	Lukáš Czerner <lczerner@...hat.com>
To:	Andreas Dilger <adilger@...ger.ca>
cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH 1/3] ext4: Verify block bitmap even after fresh
 initialization

On Mon, 1 Jun 2015, Andreas Dilger wrote:

> Date: Mon, 1 Jun 2015 13:20:31 -0600
> From: Andreas Dilger <adilger@...ger.ca>
> To: Lukas Czerner <lczerner@...hat.com>
> Cc: linux-ext4@...r.kernel.org
> Subject: Re: [PATCH 1/3] ext4: Verify block bitmap even after fresh
>     initialization
> 
> 
> > On Jun 1, 2015, at 1:54 AM, Lukas Czerner <lczerner@...hat.com> wrote:
> > 
> > If we want to rely on the buffer_verified() flag of the block bitmap
> > buffer, we have to set it consistently. However currently if we're
> > initializing uninitialized block bitmap in
> > ext4_read_block_bitmap_nowait() we're not going to set buffer verified
> > at all.
> > 
> > We can do this by simply setting the flag on the buffer, but I think
> > it's actually better to run ext4_validate_block_bitmap() to make sure
> > that what we did in the ext4_init_block_bitmap() is right.
> > 
> > So run ext4_validate_block_bitmap() even after the block bitmap
> > initialization. Also bail out early from ext4_validate_block_bitmap() if
> > we see corrupt bitmap, since we already know it's corrupt and we do not
> > need to verify that.
> > 
> > Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> > ---
> > fs/ext4/balloc.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
> > index 955bf49..cd6ea29 100644
> > --- a/fs/ext4/balloc.c
> > +++ b/fs/ext4/balloc.c
> > @@ -369,7 +369,7 @@ static void ext4_validate_block_bitmap(struct super_block *sb,
> > 	struct ext4_group_info *grp = ext4_get_group_info(sb, block_group);
> > 	struct ext4_sb_info *sbi = EXT4_SB(sb);
> > 
> > -	if (buffer_verified(bh))
> > +	if (buffer_verified(bh) || EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
> > 		return;
> > 
> > 	ext4_lock_group(sb, block_group);
> > @@ -446,7 +446,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
> > 		unlock_buffer(bh);
> > 		if (err)
> > 			ext4_error(sb, "Checksum bad for grp %u", block_group);
> > -		return bh;
> > +		goto verify;
> 
> (defect) This looks like it will miss the ext4_unlock_group() call
> below, since that is missing in the "verify:" branch.  Either you
> need to add an explicit ext4_unlock_group() call before "goto verify",
> or add a new "unlock_group:" label that unlocks the group.

Hi,

the code snippet tricked you ;). Take a look at the code there is
ext4_unlock_group() just before unlock_buffer() which is missing in
the snipper above.

Thanks!
-Lukas

> 
> 
> > 	}
> > 	ext4_unlock_group(sb, block_group);
> > 	if (buffer_uptodate(bh)) {
> 
> Cheers, Andreas
> 
> 
> 
> 
> 
> 
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