Re: [autofs] [RFC PATCH]autofs4: hang and proposed fix

[Trond Myklebust <trond.myklebust@fys.uio.no>]

On Thu, 2005-12-01 at 00:12 +0800, Ian Kent wrote:

> > 2.4 kernels did a second d_lookup() after retaking the i_sem. The
> > problem is what do you do in the case of a race: you either have to loop
> > back (may lead to infinite loops of d_lookup()+d_invalidate()) or you do
> > something like retry once, then return an error (which is what 2.4
> > kernels did).
> 
> But in this case the semaphore is already held up until the revalidate so 
> I guess the concern is that the dentry goes away after releasing the 
> semaphore?

The problem is the same: dealing with the case of someone else
populating the d_cache while you have temporarily dropped the
dir->i_sem.

> btw, a little aside.
> I'm having trouble understanding where EEXIST is returned in a call such 
> as sys_mkdir. Can you help?

The call to may_create() (at the top of vfs_mkdir()) will return EEXIST
if the dentry is already positive i.e. dentry->d_inode is non-null.

Cheers,
  Trond