From mboxrd@z Thu Jan 1 00:00:00 1970 From: annie li Subject: Re: [PATCH net] xen-netback: use jiffies_64 value to calculate credit timeout Date: Mon, 28 Oct 2013 10:36:40 +0800 Message-ID: <526DCDB8.1080908@oracle.com> References: <1382872313-11675-1-git-send-email-wei.liu2@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: xen-devel@lists.xen.org, netdev@vger.kernel.org, david.vrabel@citrix.com, jbeulich@suse.com, Ian Campbell , Jason Luan To: Wei Liu Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:43331 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754935Ab3J1Cg5 (ORCPT ); Sun, 27 Oct 2013 22:36:57 -0400 In-Reply-To: <1382872313-11675-1-git-send-email-wei.liu2@citrix.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2013-10-27 19:11, Wei Liu wrote: > time_after_eq() only works if the delta is < MAX_ULONG/2. > > For a 32bit Dom0, if netfront sends packets at a very low rate, the time > between subsequent calls to tx_credit_exceeded() may exceed MAX_ULONG/2 > and the test for timer_after_eq() will be incorrect. Credit will not be > replenished and the guest may become unable to send packets (e.g., if > prior to the long gap, all credit was exhausted). > > Use jiffies_64 variant to mitigate this problem for 32bit Dom0. > > Suggested-by: Jan Beulich > Suggested-by: David Vrabel > Signed-off-by: Wei Liu > Cc: Ian Campbell > Cc: Jason Luan > --- > drivers/net/xen-netback/common.h | 1 + > drivers/net/xen-netback/interface.c | 4 ++-- > drivers/net/xen-netback/netback.c | 13 ++++++------- > 3 files changed, 9 insertions(+), 9 deletions(-) > > diff --git a/drivers/net/xen-netback/common.h b/drivers/net/xen-netback/common.h > index 5715318..400fea1 100644 > --- a/drivers/net/xen-netback/common.h > +++ b/drivers/net/xen-netback/common.h > @@ -163,6 +163,7 @@ struct xenvif { > unsigned long credit_usec; > unsigned long remaining_credit; > struct timer_list credit_timeout; > + u64 credit_window_start; > > /* Statistics */ > unsigned long rx_gso_checksum_fixup; > diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c > index 01bb854..8c45b63 100644 > --- a/drivers/net/xen-netback/interface.c > +++ b/drivers/net/xen-netback/interface.c > @@ -312,8 +312,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid, > vif->credit_bytes = vif->remaining_credit = ~0UL; > vif->credit_usec = 0UL; > init_timer(&vif->credit_timeout); > - /* Initialize 'expires' now: it's used to track the credit window. */ > - vif->credit_timeout.expires = jiffies; > + /* credit window is tracked in credit_window_start */ > + vif->credit_window_start = get_jiffies_64(); > > dev->netdev_ops = &xenvif_netdev_ops; > dev->hw_features = NETIF_F_SG | NETIF_F_IP_CSUM | NETIF_F_TSO; > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c > index f3e591c..1bc0688 100644 > --- a/drivers/net/xen-netback/netback.c > +++ b/drivers/net/xen-netback/netback.c > @@ -1185,18 +1185,17 @@ out: > > static bool tx_credit_exceeded(struct xenvif *vif, unsigned size) > { > - unsigned long now = jiffies; > - unsigned long next_credit = > - vif->credit_timeout.expires + > - msecs_to_jiffies(vif->credit_usec / 1000); > + u64 now = get_jiffies_64(); > + u64 next_credit = vif->credit_window_start + > + (u64)msecs_to_jiffies(vif->credit_usec / 1000); You simply replace "credit_timeout.expires" with "vif->credit_window_start" here, and never update "vif->credit_window_start" in following code. > > /* Timer could already be pending in rare cases. */ > if (timer_pending(&vif->credit_timeout)) > return true; > > /* Passed the point where we can replenish credit? */ > - if (time_after_eq(now, next_credit)) { > - vif->credit_timeout.expires = now; > + if (time_after_eq64(now, next_credit)) { > + vif->credit_timeout.expires = (unsigned long)now; updates credit_window_start as following, vif->credit_window_start = (unsigned long)now; > tx_add_credit(vif); > } > > @@ -1207,7 +1206,7 @@ static bool tx_credit_exceeded(struct xenvif *vif, unsigned size) > vif->credit_timeout.function = > tx_credit_callback; > mod_timer(&vif->credit_timeout, > - next_credit); > + (unsigned long)next_credit); vif->credit_timeout.expires is unsigned long, and this still causes original issue on 32bit system, which works well on 64bit. Or rewriting code to avoid uses of vif->credit_timeout.expires, but it is complex. BTW, I prefer Luan's patch which is simple and clear. Thanks Annie