From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx3-phx2.redhat.com ([209.132.183.24]:42343 "EHLO mx3-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932227AbcJEPyy (ORCPT ); Wed, 5 Oct 2016 11:54:54 -0400 Date: Wed, 5 Oct 2016 11:54:48 -0400 (EDT) From: CAI Qian To: tj Cc: Al Viro , Linus Torvalds , Dave Chinner , linux-xfs , Jens Axboe , Nick Piggin , linux-fsdevel@vger.kernel.org Message-ID: <270577901.647921.1475682888765.JavaMail.zimbra@redhat.com> In-Reply-To: <20161005153014.GC26977@htj.duckdns.org> References: <774397084.821469.1475260403929.JavaMail.zimbra@redhat.com> <20161003013737.GR19539@ZenIV.linux.org.uk> <1937480340.100083.1475516965286.JavaMail.zimbra@redhat.com> <1812816839.401734.1475602751170.JavaMail.zimbra@redhat.com> <20161004214219.GN4205@htj.duckdns.org> <1238277728.610186.1475676579513.JavaMail.zimbra@redhat.com> <20161005153014.GC26977@htj.duckdns.org> Subject: Re: local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org List-ID: ----- Original Message ----- > From: "tj" > To: "CAI Qian" > Cc: "Al Viro" , "Linus Torvalds" , "Dave Chinner" > , "linux-xfs" , "Jens Axboe" , "Nick Piggin" > , linux-fsdevel@vger.kernel.org > Sent: Wednesday, October 5, 2016 11:30:14 AM > Subject: Re: local DoS - systemd hang or timeout (WAS: Re: [RFC][CFT] splice_read reworked) > > Hello, CAI. > > On Wed, Oct 05, 2016 at 10:09:39AM -0400, CAI Qian wrote: > > > This one seems to be the offender. cgroup is trying to offline a > > > cpuset css, which takes place under cgroup_mutex. The offlining ends > > > up trying to drain active usages of a sysctl table which apprently is > > > not happening. Did something hang or crash while trying to generate > > > sysctl content? > > > > Hmm, I am not sure, since the trinity was running from an non-privileged > > user which can only read content from /proc or /sys. > > So, userland, priviledged or not, can't cause this. The ref is held > only while the kernel code is operating to generate content or > iterating, which shouldn't be affected by userland actions. This is > caused by kernel code hanging or crashing while holding a ref. Right, the trinity calls many different random syscalls and options on those /proc/ and /sys/ files and generate lots of different errno. It is likely some of error-path out there causes hang or crash. CAI Qian