From: Trond Myklebust Subject: Re: [RFC][PATCH] nfs: don't assume fscache_acquire_cookie will always succeed Date: Wed, 20 Jan 2010 16:35:06 -0500 Message-ID: <1264023306.7799.9.camel@localhost> References: <4B56F565.7080104@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: David Howells , Linux NFS mailing list To: Suresh Jayaraman Return-path: Received: from mx2.netapp.com ([216.240.18.37]:43963 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752998Ab0ATVf5 convert rfc822-to-8bit (ORCPT ); Wed, 20 Jan 2010 16:35:57 -0500 In-Reply-To: <4B56F565.7080104@suse.de> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, 2010-01-20 at 17:51 +0530, Suresh Jayaraman wrote: > We seem to be assuming fscache_acquire_cookie will always succeed and will > obtain a valid cookie. But, under low memory conditions kmem_cache_alloc > could fail and that would leave nfsi->fscache being set to NULL. > > This could lead to a possibility of a page with PG_fscache flag set but > cookie not set(i.e. NULL). This inconsistency could trigger a kernel BUG in > nfs_fscache_release_page() and other places as we do BUG_ON(!cookie), I think. > > I'm aware that there are other places where we would need such checks, but > wanted to validate this patch before getting on to them. > > Signed-off-by: Suresh Jayaraman > --- > > fs/nfs/client.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/fs/nfs/client.c b/fs/nfs/client.c > index ee77713..7776e8a 100644 > --- a/fs/nfs/client.c > +++ b/fs/nfs/client.c > @@ -155,6 +155,8 @@ static struct nfs_client *nfs_alloc_client(const struct nfs_client_initdata *cl_ > clp->cl_machine_cred = cred; > > nfs_fscache_get_client_cookie(clp); > + if (!clp->fscache) > + goto error_cleanup; > > return clp; > That looks like it will always fail when mounting without -ofscache and/or compiling without CONFIG_NFS_FSCACHE. It seems like a better idea to have nfs_fscache_get_client_cookie() explicitly set clp->fscache to ERR_PTR(-ENOMEM) value if the fscache_acquire_cookie fails. Cheers Trond