From: Michael S. Tsirkin Date: Tue, 9 Jul 2013 10:19:18 +0000 (+0300) Subject: virtio_net: fix race in RX VQ processing X-Git-Tag: v3.2.50~56 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f5615a4ebd1ac0709a44e5fd2f638005919d71ac;p=pandora-kernel.git virtio_net: fix race in RX VQ processing commit cbdadbbf0c790f79350a8f36029208944c5487d0 upstream. virtio net called virtqueue_enable_cq on RX path after napi_complete, so with NAPI_STATE_SCHED clear - outside the implicit napi lock. This violates the requirement to synchronize virtqueue_enable_cq wrt virtqueue_add_buf. In particular, used event can move backwards, causing us to lose interrupts. In a debug build, this can trigger panic within START_USE. Jason Wang reports that he can trigger the races artificially, by adding udelay() in virtqueue_enable_cb() after virtio_mb(). However, we must call napi_complete to clear NAPI_STATE_SCHED before polling the virtqueue for used buffers, otherwise napi_schedule_prep in a callback will fail, causing us to lose RX events. To fix, call virtqueue_enable_cb_prepare with NAPI_STATE_SCHED set (under napi lock), later call virtqueue_poll with NAPI_STATE_SCHED clear (outside the lock). Reported-by: Jason Wang Tested-by: Jason Wang Acked-by: Jason Wang Signed-off-by: Michael S. Tsirkin Signed-off-by: David S. Miller [wg: Backported to 3.2] Signed-off-by: Wolfram Gloger Signed-off-by: Ben Hutchings --- Reading git-diff-tree failed