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SubjectRe: [PATCH 2/2] Re: [autofs] Bad race condition in the new autofs protocol somewhere
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On Mon, 2007-02-12 at 15:43 +0900, Ian Kent wrote:
> On Thu, 2007-02-08 at 11:33 +0900, Ian Kent wrote:
> > On Wed, 2007-02-07 at 19:18 +0100, Olivier Galibert wrote:
> > > On Thu, Feb 08, 2007 at 03:07:41AM +0900, Ian Kent wrote:
> > > > It may be better to update to a later kernel so I don't have to port the
> > > > patch to several different kernels. Is that possible?
> > >
> > > Sure, 2.6.20 or -git?
> >
> > 2.6.20 has all the patches I've proposed so far except for the one we're
> > working on so that would be best for me.
> >
> > Seems there may still be a problem with the patch so I'll let you know
> > what's happening as soon as I can.
>
> I think I'm just about done.
>
> Could you try using the two patches here against 2.6.20 please:
>
> Ian

---

--- linux-2.6.20/fs/autofs4/root.c.lookup-check-unhased 2007-02-12 13:49:46.000000000 +0900
+++ linux-2.6.20/fs/autofs4/root.c 2007-02-12 13:54:58.000000000 +0900
@@ -655,14 +655,29 @@ static struct dentry *autofs4_lookup(str

/*
* If this dentry is unhashed, then we shouldn't honour this
- * lookup even if the dentry is positive. Returning ENOENT here
- * doesn't do the right thing for all system calls, but it should
- * be OK for the operations we permit from an autofs.
+ * lookup. Returning ENOENT here doesn't do the right thing
+ * for all system calls, but it should be OK for the operations
+ * we permit from an autofs.
*/
if (dentry->d_inode && d_unhashed(dentry)) {
+ /*
+ * A user space application can (and has done in the past)
+ * remove and re-create this directory during the callback.
+ * This can leave us with an unhashed dentry, but a
+ * successful mount! So we need to perform another
+ * cached lookup in case the dentry now exists.
+ */
+ struct dentry *parent = dentry->d_parent;
+ struct dentry *new = d_lookup(parent, &dentry->d_name);
+ if (new != NULL)
+ dentry = new;
+ else
+ dentry = ERR_PTR(-ENOENT);
+
if (unhashed)
dput(unhashed);
- return ERR_PTR(-ENOENT);
+
+ return dentry;
}

if (unhashed)

-
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