linux-kernel - Re: Oops in NFSv4 server in 2.6.23.17

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Message-ID: <20080314193350.GK2119@fieldses.org>
Date:	Fri, 14 Mar 2008 15:33:50 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Lukas Hejtmanek <xhejtman@....muni.cz>
Cc:	nfsv4@...ux-nfs.org, linux-kernel@...r.kernel.org,
	Neil Brown <neilb@...e.de>
Subject: Re: Oops in NFSv4 server in 2.6.23.17

On Fri, Mar 14, 2008 at 02:14:13PM -0400, bfields wrote:
> On Thu, Mar 13, 2008 at 03:36:31PM +0100, Lukas Hejtmanek wrote:
> > Hello,
> > 
> > On Wed, Mar 12, 2008 at 12:00:07PM -0400, J. Bruce Fields wrote:
> > > In this case it looks like something in the gss context cache is bad.
> > > 
> > > I'm not sure what's going on.
> > 
> > I discovered what triggers this bug. If I have default export with secure
> > option and I try to connect from insecure port, it produces the oops.
> > If I add insecure option to the export, no oops at all and mount succeeds.
> > 
> > Also, the bug is not triggered by the first attempt but by the second one.
> > 
> > So I guess that from the first attempt there is something inserted into gss
> > context cache - error occurs (insecure attempt with the secure option), gss
> > context is removed from the cache as invalid but not completely. And the
> > second attempt does oops. Sounds reasonable for me. 
> > 
> > Hope this helps to find the bug.
> 
> That's an excellent clue, thanks.  I wonder it would be explainable by a
> reference count imbalance of some kind in fh_verify?

OK, yes, I think so.  Could you confirm whether this fixes it?

--b.

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index 1eb771d..3e6b3f4 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -232,6 +232,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
 		fhp->fh_dentry = dentry;
 		fhp->fh_export = exp;
 		nfsd_nr_verified++;
+		cache_get(&exp->h);
 	} else {
 		/*
 		 * just rechecking permissions
@@ -241,6 +242,7 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
 		dprintk("nfsd: fh_verify - just checking\n");
 		dentry = fhp->fh_dentry;
 		exp = fhp->fh_export;
+		cache_get(&exp->h);
 		/*
 		 * Set user creds for this exportpoint; necessary even
 		 * in the "just checking" case because this may be a
@@ -252,8 +254,6 @@ fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, int type, int access)
 		if (error)
 			goto out;
 	}
-	cache_get(&exp->h);
-
 
 	error = nfsd_mode_check(rqstp, dentry->d_inode->i_mode, type);
 	if (error)
--
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