linux-kernel - Re: [PATCH] hfsplus: fix concurrent acess of alloc

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Message-ID: <1392802602.32597.2.camel@ultrabook>
Date:	Wed, 19 Feb 2014 11:36:42 +0200
From:	Sougata Santra <sougata@...era.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Christoph Hellwig <hch@....de>, <linux-fsdevel@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	Vyacheslav Dubeyko <slava@...eyko.com>,
	"Joe Perches" <joe@...ches.com>,
	Alexey Khoroshilov <khoroshilov@...ras.ru>
Subject: Re: [PATCH] hfsplus: fix concurrent acess of alloc_blocks

On Tue, 2014-02-18 at 14:06 -0800, Andrew Morton wrote:
> On Mon, 17 Feb 2014 14:20:47 +0200 Sougata Santra <sougata@...era.com> wrote:
> 
> > 
> > Concurrent access to alloc_blocks in hfsplus_inode_info is
> > protected by extents_lock mutex. This patch fixes two
> > instances where alloc_blocks modification was not protected
> > with this lock. This fixes possible allocation bitmap
> > corruption in race conditions while extending and truncating
> > files.
> > 
> > ...
> >
> > --- a/fs/hfsplus/extents.c
> > +++ b/fs/hfsplus/extents.c
> > @@ -498,11 +498,13 @@ int hfsplus_file_extend(struct inode *inode)
> >  			goto insert_extent;
> >  	}
> >  out:
> > -	mutex_unlock(&hip->extents_lock);
> >  	if (!res) {
> >  		hip->alloc_blocks += len;
> > +		mutex_unlock(&hip->extents_lock);
> >  		hfsplus_mark_inode_dirty(inode, HFSPLUS_I_ALLOC_DIRTY);
> > +		return 0;
> >  	}
> > +	mutex_unlock(&hip->extents_lock);
> >  	return res;
> >  
> 
> This looks OK.
> 
> > @@ -592,9 +594,9 @@ void hfsplus_file_truncate(struct inode *inode)
> >  		hfs_brec_remove(&fd);
> >  	}
> >  	hfs_find_exit(&fd);
> > -	mutex_unlock(&hip->extents_lock);
> >  
> >  	hip->alloc_blocks = blk_cnt;
> > +	mutex_unlock(&hip->extents_lock);
> >  out:
> >  	hip->phys_size = inode->i_size;
> >  	hip->fs_blocks = (inode->i_size + sb->s_blocksize - 1) >>
> 
> But this does not.  To provide locking for
> hfsplus_inode_info.alloc_blocks, we must take the lock *before* taking
> a local copy of ->alloc_blocks.
> 
> Please review:
> 
> --- a/fs/hfsplus/extents.c~hfsplus-fix-concurrent-acess-of-alloc_blocks-fix
> +++ a/fs/hfsplus/extents.c
> @@ -556,11 +556,13 @@ void hfsplus_file_truncate(struct inode
>  
>  	blk_cnt = (inode->i_size + HFSPLUS_SB(sb)->alloc_blksz - 1) >>
>  			HFSPLUS_SB(sb)->alloc_blksz_shift;
> +
> +	mutex_lock(&hip->extents_lock);
> +
>  	alloc_cnt = hip->alloc_blocks;
>  	if (blk_cnt == alloc_cnt)
> -		goto out;
> +		goto out_unlock;
>  
> -	mutex_lock(&hip->extents_lock);
>  	res = hfs_find_init(HFSPLUS_SB(sb)->ext_tree, &fd);
>  	if (res) {
>  		mutex_unlock(&hip->extents_lock);
> @@ -594,6 +596,7 @@ void hfsplus_file_truncate(struct inode
>  	hfs_find_exit(&fd);
>  
>  	hip->alloc_blocks = blk_cnt;
> +out_unlock:
>  	mutex_unlock(&hip->extents_lock);
>  out:
>  	hip->phys_size = inode->i_size;
> _
> 
This is good, Missed it. Thank you.

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