From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8F398C43603 for ; Mon, 16 Dec 2019 07:50:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 56D2F206CB for ; Mon, 16 Dec 2019 07:50:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726676AbfLPHuJ (ORCPT ); Mon, 16 Dec 2019 02:50:09 -0500 Received: from mga09.intel.com ([134.134.136.24]:59090 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726648AbfLPHuJ (ORCPT ); Mon, 16 Dec 2019 02:50:09 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 15 Dec 2019 23:50:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,320,1571727600"; d="scan'208";a="217333770" Received: from schindhe-mobl4.ger.corp.intel.com (HELO btopel-mobl.ger.intel.com) ([10.249.32.180]) by orsmga003.jf.intel.com with ESMTP; 15 Dec 2019 23:50:04 -0800 Subject: Re: [PATCH bpf 3/4] net/i40e: Fix concurrency issues between config flow and XSK To: Maxim Mikityanskiy , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Cc: Magnus Karlsson , Jeff Kirsher , "bpf@vger.kernel.org" , "netdev@vger.kernel.org" , "intel-wired-lan@lists.osuosl.org" , "David S. Miller" , Saeed Mahameed , Alexei Starovoitov , Daniel Borkmann , Jakub Kicinski , Jesper Dangaard Brouer , John Fastabend , Jonathan Lemon , Maxim Mikityanskiy References: <20191205155028.28854-1-maximmi@mellanox.com> <20191205155028.28854-4-maximmi@mellanox.com> <121c3135-3b52-1d64-c1e0-26de38687b4f@mellanox.com> <8e8a8cc2-9347-df33-0e98-1594b6d0171d@intel.com> <85dd0047-a033-e349-077c-395da14fe82b@mellanox.com> From: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Message-ID: <25f09973-2477-00a2-ff0c-5a99bcc9cfab@intel.com> Date: Mon, 16 Dec 2019 08:50:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <85dd0047-a033-e349-077c-395da14fe82b@mellanox.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2019-12-13 18:10, Maxim Mikityanskiy wrote: > On 2019-12-11 12:08, Björn Töpel wrote: >> On 2019-12-10 15:26, Maxim Mikityanskiy wrote: >>> On 2019-12-06 11:03, Björn Töpel wrote: >>>> On Thu, 5 Dec 2019 at 16:52, Maxim Mikityanskiy >>>> wrote: >>>>> >>>>> Use synchronize_rcu to wait until the XSK wakeup function finishes >>>>> before destroying the resources it uses: >>>>> >>>>> 1. i40e_down already calls synchronize_rcu. On i40e_down either >>>>> __I40E_VSI_DOWN or __I40E_CONFIG_BUSY is set. Check the latter in >>>>> i40e_xsk_async_xmit (the former is already checked there). >>>>> >>>>> 2. After switching the XDP program, call synchronize_rcu to let >>>>> i40e_xsk_async_xmit exit before the XDP program is freed. >>>>> >>>>> 3. Changing the number of channels brings the interface down (see >>>>> i40e_prep_for_reset and i40e_pf_quiesce_all_vsi). >>>>> >>>>> 4. Disabling UMEM sets __I40E_CONFIG_BUSY, too. >>>>> >>>>> Signed-off-by: Maxim Mikityanskiy >>>>> --- >>>>>    drivers/net/ethernet/intel/i40e/i40e_main.c | 7 +++++-- >>>>>    drivers/net/ethernet/intel/i40e/i40e_xsk.c  | 4 ++++ >>>>>    2 files changed, 9 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c >>>>> b/drivers/net/ethernet/intel/i40e/i40e_main.c >>>>> index 1ccabeafa44c..afa3a99e68e1 100644 >>>>> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c >>>>> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c >>>>> @@ -6823,8 +6823,8 @@ void i40e_down(struct i40e_vsi *vsi) >>>>>           for (i = 0; i < vsi->num_queue_pairs; i++) { >>>>>                   i40e_clean_tx_ring(vsi->tx_rings[i]); >>>>>                   if (i40e_enabled_xdp_vsi(vsi)) { >>>>> -                       /* Make sure that in-progress ndo_xdp_xmit >>>>> -                        * calls are completed. >>>>> +                       /* Make sure that in-progress ndo_xdp_xmit and >>>>> +                        * ndo_xsk_async_xmit calls are completed. >>> >>> Ooops, I see now some changes were lost during rebasing. I had a version >>> of this series with ndo_xsk_async_xmit -> ndo_xsk_wakeup fixed. >>> >>>>>                            */ >>>>>                           synchronize_rcu(); >>>>>                           i40e_clean_tx_ring(vsi->xdp_rings[i]); >>>>> @@ -12545,6 +12545,9 @@ static int i40e_xdp_setup(struct i40e_vsi *vsi, >>>>>                   i40e_prep_for_reset(pf, true); >>>>> >>>>>           old_prog = xchg(&vsi->xdp_prog, prog); >>>>> +       if (old_prog) >>>>> +               /* Wait until ndo_xsk_async_xmit completes. */ >>>>> +               synchronize_rcu(); >>>> >>>> This is not needed -- please correct me if I'm missing something! If >>>> we're disabling XDP, the need_reset-clause will take care or the >>>> proper synchronization. >>> >>> Yes, it was added to cover the case of disabling XDP. I'm not sure how >>> i40e_reset_and_rebuild will help here. What I wanted to achieve is to >>> wait until all i40e_xsk_wakeups finish after setting vsi->xdp_prog = >>> NULL and before doing anything else. I don't see how >>> i40e_reset_and_rebuild helps here, but I'm not very familiar with i40e >>> code. Could you guide me through the code of i40e_reset_and_rebuild and >>> show how it takes care of the synchronization? >>> >>>> And we don't need to worry about old_prog for >>>> the swap-XDP case, >>> >>> Right. >>> >>>> because bpf_prog_put() does cleanup with >>>> call_rcu(). >>> >>> But if i40e_xsk_wakeup is not wrapped with rcu_read_lock, it won't sync >>> with it. >>> >>>> >>>>> >>>>>           if (need_reset) >>>>>                   i40e_reset_and_rebuild(pf, true, true); >>>>> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c >>>>> b/drivers/net/ethernet/intel/i40e/i40e_xsk.c >>>>> index d07e1a890428..f73cd917c44f 100644 >>>>> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c >>>>> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c >>>>> @@ -787,8 +787,12 @@ int i40e_xsk_wakeup(struct net_device *dev, u32 >>>>> queue_id, u32 flags) >>>>>    { >>>>>           struct i40e_netdev_priv *np = netdev_priv(dev); >>>>>           struct i40e_vsi *vsi = np->vsi; >>>>> +       struct i40e_pf *pf = vsi->back; >>>>>           struct i40e_ring *ring; >>>>> >>>>> +       if (test_bit(__I40E_CONFIG_BUSY, pf->state)) >>>>> +               return -ENETDOWN; >>>>> + >>>> >>>> You right that we need to check for BUSY, since the XDP ring might be >>>> stale! Thanks for catching this! Can you respin this patch, with just >>>> this hunk? (Unless I'm wrong! :-)) >>> >>> This check itself will not be enough, unless you wrap i40e_xsk_wakeup >>> with rcu_read_lock. >>> >>> i40e_xsk_wakeup does some checks in the beginning, then the main part of >>> the code goes. My assumption is that if the checks don't pass, the main >>> part will fail in some way (e.g., NULL or dangling pointer when >>> accessing the ring), otherwise you wouldn't need those checks at all. >>> Without RCU, even if you do these checks, it may still fail in the >>> following scenario: >>> >>> 1. i40e_xsk_wakeup starts running, checks the flag, the flag is set, the >>> function goes on. >>> >>> 2. The flag gets cleared. >>> >>> 3. The resources are destroyed. >>> >>> 4. i40e_xsk_wakeup tries to access the resources that were destroyed. >>> >>> I don't see anything in i40e and ixgbe that currently protects from such >>> a race condition. If I'm missing anything, please point me to it, >>> otherwise i40e_xsk_wakeup really needs to be wrapped into rcu_read_lock. >>> I would prefer to have rcu_read_lock in the kernel, so that all drivers >>> could benefit from it, because I think it's the same issue in all >>> drivers, but I'm fine with moving it to the drivers if there is a reason >>> why some drivers may not need it. >>> >>> Thanks for taking a look. Let's settle the case with Intel's drivers, so >>> that I will know what fixes to include into the respin. >>> >> >> Max, you're right. It's not correct without RCU locking. Thanks for the >> patience. >> >> For the Intel ndo_xsk_wakeup implementation we need to make sure that >> the 1. umem(socket) exists, and that the 2. XDP rings exists for the >> duration of the call. >> >> 1. In xsk_unbind_dev() the state is changed to UNBOUND and then >>    followed by synchronize_net(). It would be, as you wrote, incorrect >>    without RCU locking the ndo_xsk_wakeup() region. >> >> 2. To ensure that the XDP rings are intact for the duration of the >>    ndo_xsk_wakeup(), a synchronize_rcu() is required when the XDP >>    program is swapped out (prog->NULL). >> >> Again, both 1 and 2 requires RCU locking. >> >> What do you think about the this patch for xsk.c (and the Intel >> drivers)? It moves all ndo_xsk_wakeup calls do one place. > > Looks good, please also see a few comments below. > > Checking the __I40E_CONFIG_BUSY and __IXGBE_TX_DISABLED flags in the > wakeup functions is still required, I believe. You didn't include these > parts into your patch, I just want to make sure you don't suggest to > drop these parts of my patches. > No, you're right. I missed that! > How would you like to proceed with it? Do you want me to integrate your > changes into my patches and respin with both my and your sign-offs? > That sounds like a good plan! Let me know if you'd like me to do it, given that you're on vacation! >> >> diff --git a/drivers/net/ethernet/intel/i40e/i40e.h >> b/drivers/net/ethernet/intel/i40e/i40e.h >> index cb6367334ca7..4833187bd259 100644 >> --- a/drivers/net/ethernet/intel/i40e/i40e.h >> +++ b/drivers/net/ethernet/intel/i40e/i40e.h >> @@ -1152,7 +1152,7 @@ void i40e_set_fec_in_flags(u8 fec_cfg, u32 *flags); >> >>  static inline bool i40e_enabled_xdp_vsi(struct i40e_vsi *vsi) >>  { >> -    return !!vsi->xdp_prog; >> +    return !!READ_ONCE(vsi->xdp_prog); >>  } >> >>  int i40e_create_queue_channel(struct i40e_vsi *vsi, struct >> i40e_channel *ch); >> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c >> b/drivers/net/ethernet/intel/i40e/i40e_main.c >> index 1ccabeafa44c..fd084f03f00d 100644 >> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c >> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c >> @@ -12546,8 +12546,11 @@ static int i40e_xdp_setup(struct i40e_vsi *vsi, >> >>      old_prog = xchg(&vsi->xdp_prog, prog); >> >> -    if (need_reset) >> +    if (need_reset) { >> +        if (!prog) >> +            synchronize_rcu(); >>          i40e_reset_and_rebuild(pf, true, true); >> +    } >> >>      for (i = 0; i < vsi->num_queue_pairs; i++) >>          WRITE_ONCE(vsi->rx_rings[i]->xdp_prog, vsi->xdp_prog); >> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >> b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >> index 25c097cd8100..adff2cbcde1a 100644 >> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >> @@ -10261,7 +10261,11 @@ static int ixgbe_xdp_setup(struct net_device >> *dev, struct bpf_prog *prog) >> >>      /* If transitioning XDP modes reconfigure rings */ >>      if (need_reset) { >> -        int err = ixgbe_setup_tc(dev, adapter->hw_tcs); >> +        int err; >> + >> +        if (!prog) >> +            synchronize_rcu(); >> +        err = ixgbe_setup_tc(dev, adapter->hw_tcs); >> >>          if (err) { >>              rcu_assign_pointer(adapter->xdp_prog, old_prog); >> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c >> index 956793893c9d..dbf06c3b7061 100644 >> --- a/net/xdp/xsk.c >> +++ b/net/xdp/xsk.c >> @@ -334,12 +334,20 @@ bool xsk_umem_consume_tx(struct xdp_umem *umem, >> struct xdp_desc *desc) >>  } >>  EXPORT_SYMBOL(xsk_umem_consume_tx); >> >> -static int xsk_zc_xmit(struct xdp_sock *xs) >> +static int xsk_wakeup(struct xdp_sock *xs, u8 flags) >>  { >>      struct net_device *dev = xs->dev; >> +    int err; >> >> -    return dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id, >> -                           XDP_WAKEUP_TX); >> +    rcu_read_lock(); >> +    err = dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id, flags); >> +    rcu_read_unlock(); >> +    return err; >> +} >> + >> +static int xsk_zc_xmit(struct xdp_sock *xs) >> +{ >> +    return xsk_wakeup(xs, XDP_WAKEUP_TX); >>  } >> >>  static void xsk_destruct_skb(struct sk_buff *skb) >> @@ -453,19 +461,16 @@ static __poll_t xsk_poll(struct file *file, struct >> socket *sock, >>      __poll_t mask = datagram_poll(file, sock, wait); >>      struct sock *sk = sock->sk; >>      struct xdp_sock *xs = xdp_sk(sk); >> -    struct net_device *dev; >>      struct xdp_umem *umem; >> >>      if (unlikely(!xsk_is_bound(xs))) >>          return mask; >> >> -    dev = xs->dev; >>      umem = xs->umem; >> >>      if (umem->need_wakeup) { >> -        if (dev->netdev_ops->ndo_xsk_wakeup) >> -            dev->netdev_ops->ndo_xsk_wakeup(dev, xs->queue_id, >> -                            umem->need_wakeup); >> +        if (xs->zc) >> +            xsk_wakeup(umem->need_wakeup); > > Thanks for spotting this. I missed the second place where wakeup is called. > > BTW, does the current code contain a bug? The socket can be opened in > copy mode even if ndo_xsk_wakeup is not NULL, and we'll call > ndo_xsk_wakeup in this case, although it's not zero-copy. After your > patch it will be fixed. > Ah, yes indeed. Good catch! > P.S. I'll be on vacation, so I added my personal email to Cc to be able > to receive responses. > ACK! ...and again let me know if you'd like me to spin the patches. Cheers, Björn >>          else >>              /* Poll needs to drive Tx also in copy mode */ >>              __xsk_sendmsg(sk); >> >