Re: [PATCH] ceph: Fix oops when mounting cephfs with non-existing path

["Yan, Zheng" <zheng.z.yan@intel.com>]

On 08/17/2012 11:54 PM, Sage Weil wrote:
> Hi Yan,
> 
> On Fri, 17 Aug 2012, Yan, Zheng wrote:
>> From: "Yan, Zheng" <zheng.z.yan@intel.com>
>>
>> req->r_locked_dir is NULL if the request was created by
>> open_root_dentry(). ceph_fill_trace() lacks check for this case.
>> It causes oops when mounting cephfs with non-existing path.
> 
> This is actually an MDS bug.  The problem is that the client is issuing a 
> GETATTR request and isn't prepared to handle a dentry in the reply, but 
> the MDS sees that there is a relative path in the request and behaves like 
> this is a lookup.  We were distinguishing correctly between the two cases 
> on success, but not on error.  I've pushed branch bug-2969 to ceph.git 
> which fixes this for me.  Can you please test and verify it resolves 
> the problem?
It does resolve the problem.

> 
> We may want to have a check like the below, but it should probably be 
> accompanied by a pr_warning or WARN_ON() since it is a protocol error.  
> Generally speaking, the client isn't allowed to ignore state the MDS has 
> issued it (in this case, caps on the directory inode; lower down in 
> fill_trace possibly a dentry lease) without messing up the protocol.
> 

Thank you for your explanation. 

Yan, Zheng