From owner-freebsd-hackers@freebsd.org Thu Apr 27 12:47:09 2017 Return-Path: Delivered-To: freebsd-hackers@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id B735ED51C21; Thu, 27 Apr 2017 12:47:09 +0000 (UTC) (envelope-from alfred@freebsd.org) Received: from elvis.mu.org (elvis.mu.org [IPv6:2001:470:1f05:b76::196]) by mx1.freebsd.org (Postfix) with ESMTP id A762489; Thu, 27 Apr 2017 12:47:09 +0000 (UTC) (envelope-from alfred@freebsd.org) Received: from Alfreds-MacBook-Pro-2.local (unknown [IPv6:2601:645:8003:a4d6:7598:6ebc:285c:5f89]) by elvis.mu.org (Postfix) with ESMTPSA id 08E4B346DE24; Thu, 27 Apr 2017 05:47:09 -0700 (PDT) Subject: Re: racy tests To: Ngie Cooper , Brooks Davis References: <20170425230247.GA8201@spindle.one-eyed-alien.net> Cc: "freebsd-testing@freebsd.org" , "freebsd-hackers@freebsd.org" , Alan Somers , "bdrewery@freebsd.org" From: Alfred Perlstein Organization: FreeBSD Message-ID: <878d2f79-df2d-0c6c-bd21-c0e663160f45@freebsd.org> Date: Thu, 27 Apr 2017 05:47:11 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 27 Apr 2017 12:47:09 -0000 Can't something similar to this be done? .(05:40:37)(bright@elvis.mu.org) ~ % mkfifo derp .(05:43:46)(bright@elvis.mu.org) ~ % cat derp & [1] 59244 .(05:43:53)(bright@elvis.mu.org) ~ % ( pwait $! && echo "$?" > ex_status )& [2] 59263 .(05:44:28)(bright@elvis.mu.org) ~ % echo "hi" >> derp && echo "exit status: $(cat ex_status)" hi [2] + done ( pwait $! && echo "$?" > ex_status; ) [1] + done cat derp exit status: 0 Make a fifo, lodge a cat(1) process waiting for data, pwait in the background and stuff pwait's status into a file, then unstick the cat(1) by writing to the fifo, and then read the exit status from pwait from the file? \m/ -Alfred On 4/25/17 7:22 PM, Ngie Cooper wrote: > On Tue, Apr 25, 2017 at 4:02 PM, Brooks Davis wrote: >> I've been running the FreeBSD test suite for mips64 under qemu. As a >> result, I'm seeing some tests fail due to assumptions about timing producing >> test races. For example one of the pwait tests does this: >> >> timeout_many_body() >> { >> sleep 1 & >> p1=$! >> >> sleep 5 & >> p5=$! >> >> sleep 10 & >> p10=$! >> >> atf_check \ >> -o empty \ >> -e empty \ >> -s exit:124 \ >> timeout --preserve-status 7.5 pwait -t 6 $p1 $p5 $p10 >> } >> >> Under emulation, particularly if the host disks are busy, it's easily >> possible for the first sleep to exit before pwait actually runs. >> In practice, we could probably get away with cranking up the times a >> fair bit, but that would make the test slow and the race would still >> exist. >> >> Any thoughts about the right solution? Something not time based would >> be ideal, but then it seems like we'd need a parallel process to kill >> some of the waited for victims we quickly end up with something more >> complicated than pwait that also needs testing... > (Adding bdrewery@, testing@) > I need to think about this a bit. The issue might be that we're using > the wrong timer for sleep(1)/need to account for being interrupted. > > Needless to say, emulation really screws up timing assumptions because > virtual clocks don't function like hardware clocks. > > Thanks, > -Ngie > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" >