[{"id":1765639,"web_url":"http://patchwork.ozlabs.org/comment/1765639/","msgid":"<94e9e0f9-403a-72c7-62d2-797f6fd1bc99@fb.com>","list_archive_url":null,"date":"2017-09-08T22:38:14","subject":"Re: [net PATCH 1/3] net: rcu lock and preempt disable missing around\n\tgeneric xdp","submitter":{"id":68234,"url":"http://patchwork.ozlabs.org/api/people/68234/","name":"Alexei Starovoitov","email":"ast@fb.com"},"content":"On 9/8/17 2:00 PM, John Fastabend wrote:\n> do_xdp_generic must be called inside rcu critical section with preempt\n> disabled to ensure BPF programs are valid and per-cpu variables used\n> for redirect operations are consistent. This patch ensures this is true\n> and fixes the splat below.\n>\n> The netif_receive_skb_internal() code path is now broken into two rcu\n> critical sections. I decided it was better to limit the preempt_enable/disable\n> block to just the xdp static key portion and the fallout is more\n> rcu_read_lock/unlock calls. Seems like the best option to me.\n>\n> [ 607.596901] =============================\n> [ 607.596906] WARNING: suspicious RCU usage\n> [ 607.596912] 4.13.0-rc4+ #570 Not tainted\n> [ 607.596917] -----------------------------\n> [ 607.596923] net/core/dev.c:3948 suspicious rcu_dereference_check() usage!\n> [ 607.596927]\n> [ 607.596927] other info that might help us debug this:\n> [ 607.596927]\n> [ 607.596933]\n> [ 607.596933] rcu_scheduler_active = 2, debug_locks = 1\n> [ 607.596938] 2 locks held by pool/14624:\n> [ 607.596943] #0: (rcu_read_lock_bh){......}, at: [] ip_finish_output2+0x14d/0x890\n> [ 607.596973] #1: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x14a/0xfd0\n> [ 607.597000]\n> [ 607.597000] stack backtrace:\n> [ 607.597006] CPU: 5 PID: 14624 Comm: pool Not tainted 4.13.0-rc4+ #570\n> [ 607.597011] Hardware name: Dell Inc. Precision Tower 5810/0HHV7N, BIOS A17 03/01/2017\n> [ 607.597016] Call Trace:\n> [ 607.597027] dump_stack+0x67/0x92\n> [ 607.597040] lockdep_rcu_suspicious+0xdd/0x110\n> [ 607.597054] do_xdp_generic+0x313/0xa50\n> [ 607.597068] ? time_hardirqs_on+0x5b/0x150\n> [ 607.597076] ? mark_held_locks+0x6b/0xc0\n> [ 607.597088] ? netdev_pick_tx+0x150/0x150\n> [ 607.597117] netif_rx_internal+0x205/0x3f0\n> [ 607.597127] ? do_xdp_generic+0xa50/0xa50\n> [ 607.597144] ? lock_downgrade+0x2b0/0x2b0\n> [ 607.597158] ? __lock_is_held+0x93/0x100\n> [ 607.597187] netif_rx+0x119/0x190\n> [ 607.597202] loopback_xmit+0xfd/0x1b0\n> [ 607.597214] dev_hard_start_xmit+0x127/0x4e0\n>\n> Fixes: d445516966dc (\"net: xdp: support xdp generic on virtual devices\")\n> Fixes: b5cdae3291f7 (\"net: Generic XDP\")\n> Acked-by: Daniel Borkmann \n> Signed-off-by: John Fastabend \n\nargh, so it's due to virtual devices and loopback.\nNot pretty, but have to agree I don't see another way of fixing it.\n\nAcked-by: Alexei Starovoitov ","headers":{"Return-Path":"","X-Original-To":"patchwork-incoming@ozlabs.org","Delivered-To":"patchwork-incoming@ozlabs.org","Authentication-Results":["ozlabs.org;\n\tspf=none (mailfrom) smtp.mailfrom=vger.kernel.org\n\t(client-ip=209.132.180.67; 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a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; \n\ts=selector1-fb-com;\n\th=From:Date:Subject:Message-ID:Content-Type:MIME-Version; \n\tbh=V3panHeg9SJC6KWrE6M52Ffk377onEb5SoxqHmn6ra4=;\n\tb=G5R3kv9tyYFd/kf+8ruo571ZDnnSD7BC6hIsfG66fxTsu2lsClxJlM1pNBLYApmS6ySpL4A+Tf+OKw7B/volsNxPGpZUYPEd5vYIq8mcwjaKZVHJutQShvfeUSC7fPRVzkrmBU+tq4+fACT3mEoI48ZNtJaSzvNGAjQgsmpUFDo="],"Subject":"Re: [net PATCH 1/3] net: rcu lock and preempt disable missing around\n\tgeneric xdp","To":"John Fastabend , ","References":"<150490397545.11590.1409723973253492363.stgit@john-XPS-13-9360>\n\t<150490443011.11590.2847947557652786219.stgit@john-XPS-13-9360>","CC":", ","From":"Alexei Starovoitov ","Message-ID":"<94e9e0f9-403a-72c7-62d2-797f6fd1bc99@fb.com>","Date":"Fri, 8 Sep 2017 15:38:14 -0700","User-Agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:45.0)\n\tGecko/20100101 Thunderbird/45.8.0","MIME-Version":"1.0","In-Reply-To":"<150490443011.11590.2847947557652786219.stgit@john-XPS-13-9360>","Content-Type":"text/plain; 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