From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [net-next 02/16] ixgbe: fix spinlock recursion with netpoll and busy poll Date: Fri, 14 Mar 2014 19:08:09 -0700 Message-ID: <87siqkqkmu.fsf@xmission.com> References: <1394790446-31591-1-git-send-email-jeffrey.t.kirsher@intel.com> <1394790446-31591-3-git-send-email-jeffrey.t.kirsher@intel.com> <20140314.145850.706702494963811330.davem@davemloft.net> <87618083B2453E4A8714035B62D679924FF2B0DD@FMSMSX105.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain Cc: David Miller , "Kirsher\, Jeffrey T" , "netdev\@vger.kernel.org" , "gospo\@redhat.com" , "sassmann\@redhat.com" , "asharma\@fb.com" , "stable\@vger.kernel.org" , "Keller\, Jacob E" To: "Tantilov\, Emil S" Return-path: In-Reply-To: <87618083B2453E4A8714035B62D679924FF2B0DD@FMSMSX105.amr.corp.intel.com> (Emil S. Tantilov's message of "Fri, 14 Mar 2014 20:40:25 +0000") Sender: stable-owner@vger.kernel.org List-Id: netdev.vger.kernel.org "Tantilov, Emil S" writes: >>-----Original Message----- >>From: David Miller [mailto:davem@davemloft.net] >>Sent: Friday, March 14, 2014 11:59 AM >>To: Kirsher, Jeffrey T >>Cc: Tantilov, Emil S; netdev@vger.kernel.org; >>gospo@redhat.com; sassmann@redhat.com; asharma@fb.com; >>stable@vger.kernel.org; Keller, Jacob E >>Subject: Re: [net-next 02/16] ixgbe: fix spinlock recursion >>with netpoll and busy poll >> >>From: Jeff Kirsher >>Date: Fri, 14 Mar 2014 02:47:12 -0700 >> >>> From: Emil Tantilov >>> >>> This patch resolves a hang with busy poll when used with netconsole. >>> >>> The main change is the check for netpoll packets in ixgbe_poll() which >>> prevents a call to spin_lock_bh() while interrupts are disabled. >>> >>> In addition it removes the call to netif_rx() since netif_receive_skb() >>> can deal with netpoll packets and also replaced the global adapter flag >>> with per-q_vector bool that indicates Rx packet from netpoll which >>> should help with performance. >>> >>> CC: Arun Sharma >>> CC: stable >>> Signed-off-by: Jacob Keller >>> Signed-off-by: Emil Tantilov >>> Tested-by: Phil Schmitt >>> Signed-off-by: Jeff Kirsher >> >>Eric Biederman and co. are working to make this completely unnecessary. >> >>What is going to happen is that poll will be called with a budget of >>zero, and no RX processing will thus occur, for netpoll. >> >>Nothing in the RX path can handle being invoked from hardware >>interrupt context, so we have to prevent it completely in all >>drivers that support netpoll. > > I noticed Eric's patches and this is obviously the better way to deal > with it, but once the netpoll_rx patches are accepted will they make > it into previous stable releases? Currently kernels between 3.11 and > 3.13 (assuming Eric's changes make it into 3.14) will hang when > netpoll and busy poll are used together. A quick comment on this patch. IXGBE_FLAG_IN_NETPOLL in ixgbe (before your refinement) is harmless but complete nonsense. The napi poll methods do not get called from ndo_poll_controller. So the call of netif_rx is bunk. Before my patches go in netpoll will cause any packets processed with napi_gro_receive or netif_receive_skb while netconsole is sending a packet to be dropped, so netif_rx (which is not called) should be unnecessary. As for the netpoll hang taking the lock. I expect that the fix for handling receving packets with netpoll is simply to disable interrupts in the ixgbe_qv_lock_ family of functions, so you can handle netpoll from hard irq context. Of course that won't be needed as soon David merges my patches and but shrug. Eric