From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7DDDC433E0 for ; Tue, 23 Jun 2020 12:00:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B28A8206A5 for ; Tue, 23 Jun 2020 12:00:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592913619; bh=ZIsccA9rrUt856R3yvH99k2vhEfDCyCr+RV7GEM30Bw=; h=Subject:To:Cc:From:Date:List-ID:From; b=yx8EwL2T/z53WdbqIPQ8zPlL/W9Q8Dn5iNfHbH2+QExamOOg2H2uSjyOfPWJTJ6Pw gcucYPg8tDRMCM5a1CT6g6cInKDkGf/RSBcloKwDTlkvcCsg3DbZ6v7F+K3aqGJD7U QctI6yTNYg65vOJkV/XY7Xlww07BnVlHZTC4k5Oo= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732536AbgFWMAT (ORCPT ); Tue, 23 Jun 2020 08:00:19 -0400 Received: from forward5-smtp.messagingengine.com ([66.111.4.239]:47669 "EHLO forward5-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732439AbgFWMAS (ORCPT ); Tue, 23 Jun 2020 08:00:18 -0400 Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailforward.nyi.internal (Postfix) with ESMTP id 38E8B1940935; Tue, 23 Jun 2020 08:00:17 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute1.internal (MEProxy); Tue, 23 Jun 2020 08:00:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:message-id:mime-version:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm3; bh=6S63e/ n3vLAeYYeKGXHev0x4+1I6bWHb+i9FGryKjY4=; b=Pju5XvLw0oO8g/MFXb9G1Y Tj6ajIbsqUQRd6UGA0qNaTxj0TZsvcRI52lHZ/5gc4LfJ4h1VEEjr+HdBNWO+DdN OLnF142dH+lrnywlH49qGgCdpdD0Vvhqkb3FmTn/faZ4geWDxi17dqKcMrPartzF rw2DzZK0Q6UePLl/ELzsj2hZYsc0jyzsiCmcEn7wlWLlxeMKknYyC2sGUw1oIB4l IqEwhKb80WYVurWBvO+7Iyd/wtjcCpi1Zei18rrn10XfiicDE6qVxxZ71OioulQJ jIFNAVOe3l7YnkP9mhlm6bkGUcvxWMYIdJTkBz4EzDX4luV/KUdOC08iymOS+kaA == X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduhedrudekhedgudelucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucenucfjughrpefuvffhfffkgggtgfesthekredttd dtlfenucfhrhhomhepoehgrhgvghhkhheslhhinhhugihfohhunhgurghtihhonhdrohhr gheqnecuggftrfgrthhtvghrnhepieetveehuedvhfdtgfdvieeiheehfeelveevheejud etveeuveeludejjefgteehnecukfhppeekfedrkeeirdekledruddtjeenucevlhhushht vghrufhiiigvpeefnecurfgrrhgrmhepmhgrihhlfhhrohhmpehgrhgvgheskhhrohgrhh drtghomh X-ME-Proxy: Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) by mail.messagingengine.com (Postfix) with ESMTPA id 7FF693280068; Tue, 23 Jun 2020 08:00:16 -0400 (EDT) Subject: FAILED: patch "[PATCH] net: core: device_rename: Use rwsem instead of a seqcount" failed to apply to 4.9-stable tree To: a.darwish@linutronix.de, bigeasy@linutronix.de, dan.carpenter@oracle.com, davem@davemloft.net, lkp@intel.com, stable@vger.kernel.org Cc: From: Date: Tue, 23 Jun 2020 14:00:10 +0200 Message-ID: <1592913610191218@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 11d6011c2cf29f7c8181ebde6c8bc0c4d83adcd7 Mon Sep 17 00:00:00 2001 From: "Ahmed S. Darwish" Date: Wed, 3 Jun 2020 16:49:44 +0200 Subject: [PATCH] net: core: device_rename: Use rwsem instead of a seqcount Sequence counters write paths are critical sections that must never be preempted, and blocking, even for CONFIG_PREEMPTION=n, is not allowed. Commit 5dbe7c178d3f ("net: fix kernel deadlock with interface rename and netdev name retrieval.") handled a deadlock, observed with CONFIG_PREEMPTION=n, where the devnet_rename seqcount read side was infinitely spinning: it got scheduled after the seqcount write side blocked inside its own critical section. To fix that deadlock, among other issues, the commit added a cond_resched() inside the read side section. While this will get the non-preemptible kernel eventually unstuck, the seqcount reader is fully exhausting its slice just spinning -- until TIF_NEED_RESCHED is set. The fix is also still broken: if the seqcount reader belongs to a real-time scheduling policy, it can spin forever and the kernel will livelock. Disabling preemption over the seqcount write side critical section will not work: inside it are a number of GFP_KERNEL allocations and mutex locking through the drivers/base/ :: device_rename() call chain. >>From all the above, replace the seqcount with a rwsem. Fixes: 5dbe7c178d3f (net: fix kernel deadlock with interface rename and netdev name retrieval.) Fixes: 30e6c9fa93cf (net: devnet_rename_seq should be a seqcount) Fixes: c91f6df2db49 (sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface name) Cc: Reported-by: kbuild test robot [ v1 missing up_read() on error exit ] Reported-by: Dan Carpenter [ v1 missing up_read() on error exit ] Signed-off-by: Ahmed S. Darwish Reviewed-by: Sebastian Andrzej Siewior Signed-off-by: David S. Miller diff --git a/net/core/dev.c b/net/core/dev.c index 10684833f864..061496a1f640 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -79,6 +79,7 @@ #include #include #include +#include #include #include #include @@ -194,7 +195,7 @@ static DEFINE_SPINLOCK(napi_hash_lock); static unsigned int napi_gen_id = NR_CPUS; static DEFINE_READ_MOSTLY_HASHTABLE(napi_hash, 8); -static seqcount_t devnet_rename_seq; +static DECLARE_RWSEM(devnet_rename_sem); static inline void dev_base_seq_inc(struct net *net) { @@ -998,33 +999,28 @@ EXPORT_SYMBOL(dev_get_by_napi_id); * @net: network namespace * @name: a pointer to the buffer where the name will be stored. * @ifindex: the ifindex of the interface to get the name from. - * - * The use of raw_seqcount_begin() and cond_resched() before - * retrying is required as we want to give the writers a chance - * to complete when CONFIG_PREEMPTION is not set. */ int netdev_get_name(struct net *net, char *name, int ifindex) { struct net_device *dev; - unsigned int seq; + int ret; -retry: - seq = raw_seqcount_begin(&devnet_rename_seq); + down_read(&devnet_rename_sem); rcu_read_lock(); + dev = dev_get_by_index_rcu(net, ifindex); if (!dev) { - rcu_read_unlock(); - return -ENODEV; + ret = -ENODEV; + goto out; } strcpy(name, dev->name); - rcu_read_unlock(); - if (read_seqcount_retry(&devnet_rename_seq, seq)) { - cond_resched(); - goto retry; - } - return 0; + ret = 0; +out: + rcu_read_unlock(); + up_read(&devnet_rename_sem); + return ret; } /** @@ -1296,10 +1292,10 @@ int dev_change_name(struct net_device *dev, const char *newname) likely(!(dev->priv_flags & IFF_LIVE_RENAME_OK))) return -EBUSY; - write_seqcount_begin(&devnet_rename_seq); + down_write(&devnet_rename_sem); if (strncmp(newname, dev->name, IFNAMSIZ) == 0) { - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); return 0; } @@ -1307,7 +1303,7 @@ int dev_change_name(struct net_device *dev, const char *newname) err = dev_get_valid_name(net, dev, newname); if (err < 0) { - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); return err; } @@ -1322,11 +1318,11 @@ int dev_change_name(struct net_device *dev, const char *newname) if (ret) { memcpy(dev->name, oldname, IFNAMSIZ); dev->name_assign_type = old_assign_type; - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); return ret; } - write_seqcount_end(&devnet_rename_seq); + up_write(&devnet_rename_sem); netdev_adjacent_rename_links(dev, oldname); @@ -1347,7 +1343,7 @@ int dev_change_name(struct net_device *dev, const char *newname) /* err >= 0 after dev_alloc_name() or stores the first errno */ if (err >= 0) { err = ret; - write_seqcount_begin(&devnet_rename_seq); + down_write(&devnet_rename_sem); memcpy(dev->name, oldname, IFNAMSIZ); memcpy(oldname, newname, IFNAMSIZ); dev->name_assign_type = old_assign_type;