From owner-svn-src-head@freebsd.org Wed Jun 3 17:46:21 2020 Return-Path: Delivered-To: svn-src-head@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id AE54C33CB82; Wed, 3 Jun 2020 17:46:21 +0000 (UTC) (envelope-from vmaffione@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 49cbtj4D2cz3yDN; Wed, 3 Jun 2020 17:46:21 +0000 (UTC) (envelope-from vmaffione@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 8C1ED11E8C; Wed, 3 Jun 2020 17:46:21 +0000 (UTC) (envelope-from vmaffione@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 053HkLVh035617; Wed, 3 Jun 2020 17:46:21 GMT (envelope-from vmaffione@FreeBSD.org) Received: (from vmaffione@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 053HkLBB035616; Wed, 3 Jun 2020 17:46:21 GMT (envelope-from vmaffione@FreeBSD.org) Message-Id: <202006031746.053HkLBB035616@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: vmaffione set sender to vmaffione@FreeBSD.org using -f From: Vincenzo Maffione Date: Wed, 3 Jun 2020 17:46:21 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r361759 - head/sys/dev/netmap X-SVN-Group: head X-SVN-Commit-Author: vmaffione X-SVN-Commit-Paths: head/sys/dev/netmap X-SVN-Commit-Revision: 361759 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 03 Jun 2020 17:46:21 -0000 Author: vmaffione Date: Wed Jun 3 17:46:21 2020 New Revision: 361759 URL: https://svnweb.freebsd.org/changeset/base/361759 Log: netmap: vtnet: fix race condition in rxsync This change prevents a race that happens when rxsync dequeues N-1 rx packets (with N being the size of the netmap rx ring). In this situation, the loop exits without re-enabling the rx interrupts, thus causing the VQ to stall. MFC after: 1 week Modified: head/sys/dev/netmap/if_vtnet_netmap.h Modified: head/sys/dev/netmap/if_vtnet_netmap.h ============================================================================== --- head/sys/dev/netmap/if_vtnet_netmap.h Wed Jun 3 17:42:17 2020 (r361758) +++ head/sys/dev/netmap/if_vtnet_netmap.h Wed Jun 3 17:46:21 2020 (r361759) @@ -310,8 +310,11 @@ vtnet_netmap_rxsync(struct netmap_kring *kring, int fl /* * First part: import newly received packets. * Only accept our own buffers (matching the token). We should only get - * matching buffers. We may need to stop early to avoid hwtail to overrun - * hwcur. + * matching buffers. The hwtail should never overrun hwcur, because + * we publish only N-1 receive buffers (and non N). + * In any case we must not leave this routine with the interrupts + * disabled, pending packets in the VQ and hwtail == (hwcur - 1), + * otherwise the pending packets could stall. */ if (netmap_no_pendintr || force_update) { uint32_t hwtail_lim = nm_prev(kring->nr_hwcur, lim); @@ -320,10 +323,17 @@ vtnet_netmap_rxsync(struct netmap_kring *kring, int fl vtnet_rxq_disable_intr(rxq); nm_i = kring->nr_hwtail; - while (nm_i != hwtail_lim) { + for (;;) { int len; token = virtqueue_dequeue(vq, &len); if (token == NULL) { + /* + * Enable the interrupts again and double-check + * for more work. We can go on until we win the + * race condition, since we are not replenishing + * in the meanwhile, and thus we will process at + * most N-1 slots. + */ if (interrupts && vtnet_rxq_enable_intr(rxq)) { vtnet_rxq_disable_intr(rxq); continue; @@ -333,6 +343,11 @@ vtnet_netmap_rxsync(struct netmap_kring *kring, int fl if (unlikely(token != (void *)rxq)) { nm_prerr("BUG: RX token mismatch"); } else { + if (nm_i == hwtail_lim) { + KASSERT(false, ("hwtail would " + "overrun hwcur")); + } + /* Skip the virtio-net header. */ len -= sc->vtnet_hdr_size; if (unlikely(len < 0)) {