Re: find_fh_dentry returned a DISCONNECTED directory

[Josef Bacik <jbacik@fb.com>]

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On 02/13/2014 10:30 PM, J. Bruce Fields wrote:
> On Thu, Feb 13, 2014 at 03:45:16PM -0800, Eric W. Biederman wrote:
>> "J. Bruce Fields" <bfields@fieldses.org> writes:
>> 
>>> Yesterday you passed on a report of this printk from nfsdfh.c
>>> firing:
>>> 
>>> printk("nfsd: find_fh_dentry returned a DISCONNECTED directory:
>>> %pd2\n", dentry);
>>> 
>>> I think the dentry probably comes from the FILEID_ROOT case
>>> of:
>>> 
>>> if (fileid_type == FILEID_ROOT) dentry =
>>> dget(exp->ex_path.dentry); else { dentry =
>>> exportfs_decode_fh(exp->ex_path.mnt, fid, data_left,
>>> fileid_type, nfsd_acceptable, exp); }
>>> 
>>> In that case the dentry was found using ordinary filesystem
>>> lookups, so doesn't go through the same DISCONNECTED-clearing
>>> logic as in the case of lookups by filehandle.
>>> 
>>> Probably they have an export root that's not a filesystem root,
>>> and the lookups happened in the right order?
>>> 
>>> I suspect that's fine, and that the printk is just stupid, but
>>> maybe we should clear DISCONNECTED when possible on normal
>>> lookups.  The following is my attempt, though I'm not sure if
>>> d_alloc is the right place to do this.  In any case it might
>>> help confirm this is what's happening.
>>> 
>>> So if you pass along this patch to the person who was seeing
>>> that printk I'd be interested in the results.
>> 
>> I have been reading through the dentry code for other reasons and
>> your patch definitely won't change anything. __d_alloc sets
>> d_flags = 0. Therefore d_alloc always returns with d_flags == 0.
> 
> You're right, of course.  I wasn't thinking straight.
> 
> So the only dentries with DISCONNECTED set are those created with 
> d_obtain_alias, which is normally only used when you're looking up
> by filehandle.
> 
> Except btrfs has a weird use in get_default_root().  So maybe they
> were running into the dentry that created?
> 
> So btrfs should probably be using something else, I'm not sure
> what.
> 

Urgh sorry for the wild goose chase Bruce, I'll fix this up,

Josef
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