Messages in this thread | | | From | Roman Gushchin <> | Subject | Re: ptrace/strace and freezer oddities and v5.2+ kernels | Date | Wed, 2 Oct 2019 02:01:06 +0000 |
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On Tue, Oct 01, 2019 at 12:14:18PM -0400, Bruce Ashfield wrote: > Hi all, >
Hi Bruce!
> The Yocto project has an upcoming release this fall, and I've been trying to > sort through some issues that are happening with kernel 5.2+ .. although > there is a specific yocto kernel, I'm testing and seeing this with > normal / vanilla > mainline kernels as well. > > I'm running into an issue that is *very* similar to the one discussed in the > [REGRESSION] ptrace broken from "cgroup: cgroup v2 freezer" (76f969e) > thread from this past may: https://lkml.org/lkml/2019/5/12/272 > > I can confirm that I have the proposed fix for the initial regression report in > my build (05b2892637 [signal: unconditionally leave the frozen state > in ptrace_stop()]), > but yet I'm still seeing 3 or 4 minute runtimes on a test that used to take 3 or > 4 seconds.
So, the problem is that you're experiencing a severe performance regression in some test, right?
> > This isn't my normal area of kernel hacking, so I've so far come up empty > at either fixing it myself, or figuring out a viable workaround. (well, I can > "fix" it by remove the cgroup_enter_frozen() call in ptrace_stop ... > but obviously, > that is just me trying to figure out what could be causing the issue). > > As part of the release, we run tests that come with various applications. The > ptrace test that is causing us issues can be boiled down to this: > > $ cd /usr/lib/strace/ptest/tests > $ time ../strace -o log -qq -esignal=none -e/clock ./printpath-umovestr>ttt > > (I can provide as many details as needed, but I wanted to keep this initial > email relatively short). > > I'll continue to debug and attempt to fix this myself, but I grabbed the > email list from the regression report in May to see if anyone has any ideas > or angles that I haven't covered in my search for a fix.
I'm definitely happy to help, but it's a bit hard to say anything from what you've provided. I'm not aware of any open issues with the freezer except some spurious cgroup frozen<->not frozen transitions which can happen in some cases. If you'll describe how can I reproduce the issue, and I'll try to take a look asap.
Roman
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