From owner-svn-src-head@freebsd.org Sat Feb 17 18:43:04 2018 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 5F1C6F02DA6; Sat, 17 Feb 2018 18:43:04 +0000 (UTC) (envelope-from pho@holm.cc) Received: from relay01.pair.com (relay01.pair.com [209.68.5.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id EF1F28DF30; Sat, 17 Feb 2018 18:43:03 +0000 (UTC) (envelope-from pho@holm.cc) Received: from x2.osted.lan (87-58-223-204-dynamic.dk.customer.tdc.net [87.58.223.204]) by relay01.pair.com (Postfix) with ESMTP id 3D46AD00389; Sat, 17 Feb 2018 13:43:02 -0500 (EST) Received: from x2.osted.lan (localhost [127.0.0.1]) by x2.osted.lan (8.14.9/8.14.9) with ESMTP id w1HIgxvc084093 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Sat, 17 Feb 2018 19:42:59 +0100 (CET) (envelope-from pho@x2.osted.lan) Received: (from pho@localhost) by x2.osted.lan (8.14.9/8.14.9/Submit) id w1HIgxZE084090; Sat, 17 Feb 2018 19:42:59 +0100 (CET) (envelope-from pho) Date: Sat, 17 Feb 2018 19:42:59 +0100 From: Peter Holm To: Mateusz Guzik Cc: Konstantin Belousov , Mateusz Guzik , src-committers , svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r329448 - head/sys/kern Message-ID: <20180217184259.GA84054@x2.osted.lan> References: <201802170848.w1H8mkfb081764@repo.freebsd.org> <20180217112738.GO94212@kib.kiev.ua> <20180217162632.GQ94212@kib.kiev.ua> <20180217163822.GA81555@x2.osted.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.25 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 17 Feb 2018 18:43:04 -0000 On Sat, Feb 17, 2018 at 06:34:34PM +0100, Mateusz Guzik wrote: > On Sat, Feb 17, 2018 at 5:38 PM, Peter Holm wrote: > > > On Sat, Feb 17, 2018 at 06:26:32PM +0200, Konstantin Belousov wrote: > > > On Sat, Feb 17, 2018 at 05:07:07PM +0100, Mateusz Guzik wrote: > > > > On Sat, Feb 17, 2018 at 01:27:38PM +0200, Konstantin Belousov wrote: > > > > > On Sat, Feb 17, 2018 at 08:48:46AM +0000, Mateusz Guzik wrote: > > > > > > Author: mjg > > > > > > Date: Sat Feb 17 08:48:45 2018 > > > > > > New Revision: 329448 > > > > > > URL: https://svnweb.freebsd.org/changeset/base/329448 > > > > > > > > > > > > Log: > > > > > > exit: get rid of PROC_SLOCK when checking a process to report > > > > > Was this tested ? > > > > > > > > > > > > > I was trussing multithreaded microbenchmarks, no issues. > > > > > > > > > In particular, are you aware of r309539 ? > > > > > > > > > > > > > So it looks like I misread the code - I have grepped > > > > thread_suspend_switch operating with the proc locked and misread > > > > thread_suspend_one's assert as PROC_LOCK_ASSERT. > > > > > > > > That said, I think this is harmless. Regardless of the lock the > > > > inspecting thread can race and check "too soon". Even for a case where > > > > it decides to report, I don't see anything which would depend on the > > > > suspending thread to finish. > > > It was definitely not harmless when I tried to avoid the spin lock there, > > > but I do not remember exact failure mode. Most likely, it was a missed > > > report of the traced child indeed, but I am not sure that truss triggered > > > it. Most likely, Peter Holm was the reporter, since he is listed in > > > the commit. > > > > > > > I ran a truss(1) test on r329456 and it fails. I have not had a > > chance to look closer at this, but this is what I see: > > > > [root@mercat1 /home/pho]# pgrep truss | xargs ps -Hlp > > UID PID PPID CPU PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND > > 0 41149 41118 0 52 0 11532 2588 wait I 0 0:01.38 truss > > /tmp/ttruss 10 > > 0 41151 41149 0 52 0 13156 2300 - TX 0 0:00.98 /tmp/ttruss > > 10 > > 0 41151 41149 0 52 0 13156 2300 - TX 0 0:00.00 /tmp/ttruss > > 10 > > [root@mercat1 /home/pho]# procstat -k 41151 > > PID TID COMM TDNAME KSTACK > > 41151 100211 ttruss - mi_switch > > thread_suspend_switch ptracestop amd64_syscall fast_syscall_common > > 41151 100765 ttruss - mi_switch > > thread_suspend_check ast doreti_ast > > [root@mercat1 /home/pho]# > > > > > Ok, I reproduced the bug with your script. I reverted the change. > > The patch I mailed in this thread fixes it for me. Below is a variant > which can be applied on top of fresh head: > > https://people.freebsd.org/~mjg/wait6_slock.diff > Yes, this also works for me with the truss(1) test scenario. Would you like me to run the full set of test? - Peter