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Re: [Cluster-devel] [GFS2 PATCH] GFS2: attempt to access beyond end of device creating file



----- Original Message -----
| Hi,
| 
| On Tue, 2012-03-13 at 13:55 -0400, Bob Peterson wrote:
| > Hi,
| > 
| > This patch initializes the hash table cache when inodes are
| > created in order to prevent using a hash table pointer left over
| > from a previous inode. It also adds boundary checking on the
| > hash table.
| > 
| > Regards,
| > 
| > Bob Peterson
| > Red Hat File Systems
| > 
| > Signed-off-by: Bob Peterson <rpeterso redhat com>
| > --
| > diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
| > index c35573a..c2eb20f 100644
| > --- a/fs/gfs2/dir.c
| > +++ b/fs/gfs2/dir.c
| > @@ -740,6 +740,7 @@ static int get_leaf_nr(struct gfs2_inode *dip,
| > u32 index,
| >  	hash = gfs2_dir_get_hash_table(dip);
| >  	if (IS_ERR(hash))
| >  		return PTR_ERR(hash);
| > +	BUG_ON(index >= (1 << dip->i_depth));
| >  	*leaf_out = be64_to_cpu(*(hash + index));
| >  	return 0;
| >  }
| > diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
| > index 6172fa7..bd2abe3 100644
| > --- a/fs/gfs2/super.c
| > +++ b/fs/gfs2/super.c
| > @@ -1576,6 +1576,7 @@ static struct inode *gfs2_alloc_inode(struct
| > super_block *sb)
| >  		ip->i_flags = 0;
| >  		ip->i_gl = NULL;
| >  		ip->i_rgd = NULL;
| > +		ip->i_hash_cache = NULL;
| >  	}
| >  	return &ip->i_inode;
| >  }
| > 
| 
| The question is how does this pointer land up being not NULL to start
| with... I thought that you were looking into that from your earlier
| comment in the bug,
| 
| Steve.
Hi,

My belief is that the i_hash_cache pointer was non-NULL because of
a code path in the RHEL6 kernel that does not exist in the upstream
kernel. (RHEL6 function gfs2_clear_inode was not invalidating the hash
table cache like it should, but it doesn't exist in upstream GFS2).

If my suspicion is correct, setting the i_hash_cache pointer to NULL
from gfs2_alloc_inode is unnecessary and purely precautionary.
I'm running some tests on the RHEL6 kernel to help prove that theory,
but the test will probably take all day (it's a long-running test).

I can't reproduce the original problem with the upstream kernel
because I can't run that test on my upstream box (it requires a
special RHEL6 environment set up by a third party).

Regards,

Bob Peterson
Red Hat File Systems


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