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From: David Howells <dhowells@redhat.com>
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To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: dhowells@redhat.com, torvalds@linux-foundation.org,
        linux-fsdevel@vger.kernel.org, linux-afs@lists.infradead.org,
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Subject: Re: [PATCH 05/20] afs: Implement @sys substitution handling
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Date: Fri, 06 Apr 2018 09:08:55 +0100
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Al Viro <viro@ZenIV.linux.org.uk> wrote:

> > +static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry,
> > +				       struct key *key)
> > +{
> 
> > +		ret = lookup_one_len(buf, parent, len);
> 
> Er...  Parent is locked only shared here and lookup_one_len() seriously
> depends upon exclusive lock.  As it is, race with lookup of the full name
> will mess the things up very badly.

How should it be done?  Do I have to use d_alloc_parallel(), analogous to
lookup_slow() without taking the rwsem again?

David

PS: Can you stick a banner comment on d_alloc_parallel() describing it?