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Date: Thu, 10 Dec 2015 00:48:51 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: linux-next@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mike Marshall <hubcap@omnibond.com>
Subject: Re: linux-next: build failure after merge of the vfs tree
Message-ID: <20151210004851.GB20997@ZenIV.linux.org.uk>
References: <20151210111847.07db6062@canb.auug.org.au>
 <20151210112322.16081535@canb.auug.org.au>
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On Thu, Dec 10, 2015 at 11:23:22AM +1100, Stephen Rothwell wrote:
> [Just adding the origefs maintainer to the cc list]
> > -static const char *pvfs2_follow_link(struct dentry *dentry, void **cookie)
> > +static const char *pvfs2_get_link(struct dentry *dentry, struct inode *inode,
> > +				  void **cookie)
> >  {
> > -	char *target =  PVFS2_I(dentry->d_inode)->link_target;

Better fix is to have inode->link = PVFS2_I(dentry->d_inode)->link_target;
when we set the latter and use .get_link = simple_get_link...

Said that, there is an unpleasant bug in that area - link_target of a live
inode can be overwritten, right under the pathname resolution walking the
old contents of that thing.

copy_attributes_to_inode() is triggered by ->d_revalidate() and by ->getattr()
and it's really, really unsafe for a live inode.  Just look what it does
to ->i_mode...  Sure, normally a server won't return different symlink bodies
on subsequent getattr requests.  As long as it's sane (and not compromised,
etc.), but relying upon that is not a good idea.