From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9586828DA0 for ; Fri, 28 Jun 2024 03:49:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719546544; cv=none; b=YpA7u1On0oitkXkxgKU9kTLRUY7OT2ZqvB6wqouh1LnZRV7yswnwB+zHSpVVrPjAcvJ1VuwnKBtSt+NGzJXu5ZPINDgfIaOYx07v7z0IYdXzfx63T3Q4FZavDwIm/9x3IawzJfFuQ5HrElct/8fZPuzvLpC15gn1S4nr6wgoIcU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719546544; c=relaxed/simple; bh=rszzRqErICJL8JOWOIVe1BACg60UpZv1vWSeKZALa7k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VU98jM+0bBTX/hNhkHje7qlWmiRrq+2IqmZMjSZE+1Y32Sgh8MfvOcrG47adNm0Dz7CKS0cAFQGcepORXgYpLWjFMiEB2qB6rleOWLi2QhazAkgU1mUz6OD2VuBRWIE9ynDE2SMm02ZaKNrgAOAEPfziDFzmsGbP8tO4L4aighQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=b+SQZsOm; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="b+SQZsOm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id ECC4CC2BBFC; Fri, 28 Jun 2024 03:49:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1719546544; bh=rszzRqErICJL8JOWOIVe1BACg60UpZv1vWSeKZALa7k=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=b+SQZsOmoibvsEtxNvd7V5IqQ1qMruyUk1z8OEkv9uC7+JuPTo1XrewyI40xJirzy u1SI0FUkhTtROKkQmOD+qC8yJfeHB86f5BbQwaD8pSlA3d4da12CdqufKBKXTBcRlW OlHBAX63ODZUQGI56wy9DeAPtpKcPgc8U1YN4k2fXHvG71uY/kynZSVn+G+PnQc1ei MI1ZXoBeYeO0ayvqD51X9BCHAaQKr7lFMT7WqETF0vR1R2eiIMEgjQn2cdvU9x0H4x 5iN5KWBuEdL89Y8P6//FXTObFfRWSiWHNEGcAwJF5flA2oOy6Is9D4Rev0+w+Sq2/w y8BcHO+oUfS2A== Date: Thu, 27 Jun 2024 23:49:02 -0400 From: Mike Snitzer To: NeilBrown Cc: Jeff Layton , linux-nfs@vger.kernel.org, Chuck Lever , Trond Myklebust , snitzer@hammerspace.com Subject: Re: [PATCH v8 09/18] nfsd: use percpu_ref to interlock nfsd_destroy_serv and nfsd_open_local_fh Message-ID: References: <> <70a92bcf0e6ad3e7ef9fa96edf68d9cdb32e6a2e.camel@kernel.org> <171954601675.16071.8822404139869125051@noble.neil.brown.name> Precedence: bulk X-Mailing-List: linux-nfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <171954601675.16071.8822404139869125051@noble.neil.brown.name> On Fri, Jun 28, 2024 at 01:40:16PM +1000, NeilBrown wrote: > On Fri, 28 Jun 2024, Jeff Layton wrote: > > On Thu, 2024-06-27 at 13:14 -0400, Mike Snitzer wrote: > > > On Thu, Jun 27, 2024 at 07:24:54AM -0400, Jeff Layton wrote: > > > > On Wed, 2024-06-26 at 14:24 -0400, Mike Snitzer wrote: > > > > > Introduce nfsd_serv_get and nfsd_serv_put and update the nfsd > > > > > code to > > > > > prevent nfsd_destroy_serv from destroying nn->nfsd_serv until any > > > > > client initiated localio calls to nfsd (that are _not_ in the > > > > > context > > > > > of nfsd) are complete. > > > > > > > > > > nfsd_open_local_fh is updated to nfsd_serv_get before opening its > > > > > file > > > > > handle and then drop the reference using nfsd_serv_put at the end > > > > > of > > > > > nfsd_open_local_fh. > > > > > > > > > > This "interlock" working relies heavily on nfsd_open_local_fh()'s > > > > > maybe_get_net() safely dealing with the possibility that the > > > > > struct > > > > > net (and nfsd_net by association) may have been destroyed by > > > > > nfsd_destroy_serv() via nfsd_shutdown_net(). > > > > > > > > > > Verified to fix an easy to hit crash that would occur if an nfsd > > > > > instance running in a container, with a localio client mounted, > > > > > is > > > > > shutdown. Upon restart of the container and associated nfsd the > > > > > client > > > > > would go on to crash due to NULL pointer dereference that > > > > > occuured due > > > > > to the nfs client's localio attempting to nfsd_open_local_fh(), > > > > > using > > > > > nn->nfsd_serv, without having a proper reference on nn- > > > > > >nfsd_serv. > > > > > > > > > > Signed-off-by: Mike Snitzer > > > > > --- > > > > >  fs/nfsd/localio.c |  2 ++ > > > > >  fs/nfsd/netns.h   |  8 +++++++- > > > > >  fs/nfsd/nfssvc.c  | 39 +++++++++++++++++++++++++++++++++++++++ > > > > >  3 files changed, 48 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c > > > > > index 48118db801b5..819589ae2008 100644 > > > > > --- a/fs/nfsd/localio.c > > > > > +++ b/fs/nfsd/localio.c > > > > > @@ -204,6 +204,7 @@ int nfsd_open_local_fh(struct net *net, > > > > >   } > > > > >   nn = net_generic(net, nfsd_net_id); > > > > >   > > > > > + nfsd_serv_get(nn); > > > > >   serv = READ_ONCE(nn->nfsd_serv); > > > > >   if (unlikely(!serv)) { > > > > >   dprintk("%s: localio denied. Server not > > > > > running\n", __func__); > > > > > @@ -244,6 +245,7 @@ int nfsd_open_local_fh(struct net *net, > > > > >  out_revertcred: > > > > >   revert_creds(save_cred); > > > > >  out_net: > > > > > + nfsd_serv_put(nn); > > > > >   put_net(net); > > > > >   return status; > > > > >  } > > > > > diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h > > > > > index 0c5a1d97e4ac..17a73c780ca1 100644 > > > > > --- a/fs/nfsd/netns.h > > > > > +++ b/fs/nfsd/netns.h > > > > > @@ -13,6 +13,7 @@ > > > > >  #include > > > > >  #include > > > > >  #include > > > > > +#include > > > > >  #include > > > > >  #include > > > > >  #include > > > > > @@ -140,7 +141,9 @@ struct nfsd_net { > > > > >   > > > > >   struct svc_info nfsd_info; > > > > >  #define nfsd_serv nfsd_info.serv > > > > > - > > > > > + struct percpu_ref nfsd_serv_ref; > > > > > + struct completion nfsd_serv_confirm_done; > > > > > + struct completion nfsd_serv_free_done; > > > > >   > > > > >   /* > > > > >   * clientid and stateid data for construction of net > > > > > unique COPY > > > > > @@ -225,6 +228,9 @@ struct nfsd_net { > > > > >  extern bool nfsd_support_version(int vers); > > > > >  extern void nfsd_netns_free_versions(struct nfsd_net *nn); > > > > >   > > > > > +void nfsd_serv_get(struct nfsd_net *nn); > > > > > +void nfsd_serv_put(struct nfsd_net *nn); > > > > > + > > > > >  extern unsigned int nfsd_net_id; > > > > >   > > > > >  void nfsd_copy_write_verifier(__be32 verf[2], struct nfsd_net > > > > > *nn); > > > > > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c > > > > > index a477d2c5088a..be5acb7a4057 100644 > > > > > --- a/fs/nfsd/nfssvc.c > > > > > +++ b/fs/nfsd/nfssvc.c > > > > > @@ -258,6 +258,30 @@ int nfsd_minorversion(struct nfsd_net *nn, > > > > > u32 minorversion, enum vers_op change > > > > >   return 0; > > > > >  } > > > > >   > > > > > +void nfsd_serv_get(struct nfsd_net *nn) > > > > > +{ > > > > > + percpu_ref_get(&nn->nfsd_serv_ref); > > > > > +} > > > > > + > > > > > +void nfsd_serv_put(struct nfsd_net *nn) > > > > > +{ > > > > > + percpu_ref_put(&nn->nfsd_serv_ref); > > > > > +} > > > > > + > > > > > +static void nfsd_serv_done(struct percpu_ref *ref) > > > > > +{ > > > > > + struct nfsd_net *nn = container_of(ref, struct nfsd_net, > > > > > nfsd_serv_ref); > > > > > + > > > > > + complete(&nn->nfsd_serv_confirm_done); > > > > > +} > > > > > + > > > > > +static void nfsd_serv_free(struct percpu_ref *ref) > > > > > +{ > > > > > + struct nfsd_net *nn = container_of(ref, struct nfsd_net, > > > > > nfsd_serv_ref); > > > > > + > > > > > + complete(&nn->nfsd_serv_free_done); > > > > > +} > > > > > + > > > > >  /* > > > > >   * Maximum number of nfsd processes > > > > >   */ > > > > > @@ -462,6 +486,7 @@ static void nfsd_shutdown_net(struct net > > > > > *net) > > > > >   lockd_down(net); > > > > >   nn->lockd_up = false; > > > > >   } > > > > > + percpu_ref_exit(&nn->nfsd_serv_ref); > > > > >  #if IS_ENABLED(CONFIG_NFSD_LOCALIO) > > > > >   list_del_rcu(&nn->nfsd_uuid.list); > > > > >  #endif > > > > > @@ -544,6 +569,13 @@ void nfsd_destroy_serv(struct net *net) > > > > >   struct nfsd_net *nn = net_generic(net, nfsd_net_id); > > > > >   struct svc_serv *serv = nn->nfsd_serv; > > > > >   > > > > > + lockdep_assert_held(&nfsd_mutex); > > > > > + > > > > > + percpu_ref_kill_and_confirm(&nn->nfsd_serv_ref, > > > > > nfsd_serv_done); > > > > > + wait_for_completion(&nn->nfsd_serv_confirm_done); > > > > > + wait_for_completion(&nn->nfsd_serv_free_done); > > > > > + /* percpu_ref_exit is called in nfsd_shutdown_net */ > > > > > + > > > > > > > > At this point where you're waiting on these completion vars, what > > > > stops > > > > the client from issuing new localio requests? > > > > > > The server going down.  The interlock is with nfsd_open_local_fh, so > > > once any active file opens complete the server will get these > > > completions and the server will go down.  The client will reconnect > > > if/when the server comes back up. > > > > > > Maybe I'm not imaginative enough, but is there risk of never-ending > > > overlapping file opens that prevent nfsd_destroy_serv() from > > > progressing? > > > > > > > Yeah, I think it's a possibility, especially if the underlying > > filesystem is particularly slow. You can probably solve that by just > > not handing out new references somehow once you're going to call > > percpu_ref_kill_and_confirm. > > percpu-refcount has just to tool you need. > > Use percpu_ref_tryget_live(). nfsd_serv_get() must be able to fail, and > so it must use this. If it does then it can safely read ->nfsd_serv > without checking for NULL. Indeed, I am actively coding the switch to using percpu_ref_tryget_live, so your message confirming I was on the right track is both timely and helpful.