Messages in this thread | | | From | Blaisorblade <> | Subject | Re: [uml-devel] Re: [PATCH 12/12] HPPFS: fix nameidata handling | Date | Wed, 21 Sep 2005 18:34:11 +0200 |
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On Wednesday 21 September 2005 05:54, Al Viro wrote: > On Sun, Sep 18, 2005 at 04:10:09PM +0200, Paolo 'Blaisorblade' Giarrusso wrote: > > From: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
> > In follow_link, we call the underlying method with the same nameidata we > > got - it will then call path_release() and then dput()/mntput() on hppfs > > dentries / vfsmount rather than his own, which could be problematic (I'm > > not really sure, however).
> Don't bother with that, procfs doesn't and will not care anyway. It _is_ > legal to pass NULL as nd, Where? At least not in proc_follow_link, I don't know for the rest.
I'm now seeing lookup_one_len doing exactly that. But still, could these conventions be documented, as they're surely untrivial to guess?
> so you've actually introduced breakage here. > Just pass NULL and be done with that.
> > @@ -213,11 +240,20 @@ static struct dentry *hppfs_lookup(struc > > } else { > > up(&parent->d_inode->i_sem); > > if (proc_dentry->d_op && proc_dentry->d_op->d_revalidate) { > > - if (!proc_dentry->d_op->d_revalidate(proc_dentry, NULL) && > > + sav_dentry = nd->dentry; > > + sav_mnt = nd->mnt; > > + > > + nd->dentry = dget(proc_dentry); > > + nd->mnt = mntget(proc_submnt); > > + if (!proc_dentry->d_op->d_revalidate(proc_dentry, nd) && > > !d_invalidate(proc_dentry)) { > > dput(proc_dentry); > > proc_dentry = ERR_PTR(-ENOENT); > > } > > + path_release(nd); > > + > > + nd->dentry = sav_dentry; > > + nd->mnt = sav_mnt; > > } > > }
> Shouldn't be there at all (use lookup_one_len() instead of open-coding it)
> > static struct inode_operations hppfs_file_iops = { > > @@ -794,6 +846,9 @@ static int hppfs_readlink(struct dentry > > > > static void* hppfs_follow_link(struct dentry *dentry, struct nameidata > > *nd) { > > + struct dentry *sav_dentry; > > + struct vfsmount *sav_mnt; > > + [...] > And this is absolutely bogus. The whole point of ->follow_link() is to > move where your nameidata points to. So no, you do _not_ want to flip > nameidata, you do not want to drop it and you certainly do not want > to flip it back. Just call the underlying one. But wouldn't the callee expect that nd->dentry is the same thing which I pass?
Yes, nameidata has other fields too, but is ->dentry meant to be unused here? Not surely.
And especially, how would proc_pid_follow_link()'s path_release() call handle that?
I've been suspicious that, indeed, recursive lookup holds a ref on each pathname component dentry, and that proc, in that case, knows it can do without.
-- Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!". Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894) http://www.user-mode-linux.org/~blaisorblade
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