From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH v3.10-rc7] net: fix kernel deadlock with interface rename and netdev name retrieval. Date: Wed, 26 Jun 2013 09:33:34 -0700 Message-ID: <1372264414.3301.198.camel@edumazet-glaptop> References: <1372260222-8597-1-git-send-email-nschichan@freebox.fr> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, "David S. Miller" , Eric Dumazet , Cong Wang To: Nicolas Schichan Return-path: In-Reply-To: <1372260222-8597-1-git-send-email-nschichan@freebox.fr> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, 2013-06-26 at 17:23 +0200, Nicolas Schichan wrote: > When the kernel (compiled with CONFIG_PREEMPT=n) is performing the > rename of a network interface, it can end up waiting for a workqueue > to complete. If userland is able to invoke a SIOCGIFNAME ioctl or a > SO_BINDTODEVICE getsockopt in between, the kernel will deadlock due to > the fact that read_secklock_begin() will spin forever waiting for the > writer process (the one doing the interface rename) to update the > devnet_rename_seq sequence. > > This patch fixes the problem by adding a helper (netdev_get_name()) > and using it in the code handling the SIOCGIFNAME ioctl and > SO_BINDTODEVICE setsockopt. > > The netdev_get_name() helper uses raw_seqcount_begin() to avoid > spinning forever, waiting for devnet_rename_seq->sequence to become > even. cond_resched() is used in the contended case, before retrying > the access to give the writer process a chance to finish. > > The use of raw_seqcount_begin() will incur some unneeded work in the > reader process in the contended case, but this is better than > deadlocking the system. > > Signed-off-by: Nicolas Schichan > --- This goes back to commit c91f6df2db49 ("sockopt: Change getsockopt() of SO_BINDTODEVICE to return an interface name") in linux-3.8 Acked-by: Eric Dumazet Thanks Nicolas