linux-kernel - Re: [PATCH v3 0/4] kmod: help make deterministic

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Date:   Tue, 27 Jun 2017 17:26:05 +0200
From:   Jessica Yu <jeyu@...hat.com>
To:     "Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Josh Triplett <josh@...htriplett.org>, martin.wilck@...e.com,
        Michal Marek <mmarek@...e.com>, Petr Mladek <pmladek@...e.com>,
        hare <hare@...e.com>, rwright@....com,
        Jeff Mahoney <jeffm@...e.com>, David Sterba <DSterba@...e.com>,
        Filipe Manana <fdmanana@...e.com>, NeilBrown <neilb@...e.com>,
        Guenter Roeck <linux@...ck-us.net>, rgoldwyn@...e.com,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>,
        Heinrich Schuchardt <xypron.glpk@....de>,
        Aaron Tomlin <atomlin@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ingo Molnar <mingo@...hat.com>,
        Alan Cox <alan@...ux.intel.com>, Ted Ts'o <tytso@....edu>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kselftest@...r.kernel.org,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/4] kmod: help make deterministic

+++ Luis R. Rodriguez [27/06/17 00:44 +0200]:
>On Mon, Jun 26, 2017 at 11:37:36PM +0200, Jessica Yu wrote:
>> +++ Kees Cook [20/06/17 17:23 -0700]:
>> > On Tue, Jun 20, 2017 at 1:56 PM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
>> > > On Fri, May 26, 2017 at 02:12:24PM -0700, Luis R. Rodriguez wrote:
>> > > > This v3 nukes the proc sysctl interface in favor for just letting userspace
>> > > > just check kernel revision. Prior to whenever this is merged userspace should
>> > > > try to avoid hammering more than 50 kmod threads as they can fail and it'd
>> > > > get -ENOMEM.
>> > > >
>> > > > We do away with the old heuristics on assuming you could end up with
>> > > > less than max_threads/2 < 50 threads as Dmitry notes this would mean having
>> > > > a system with 16 MiB of RAM with modules enabled. It simplifies our patch
>> > > > "kmod: reduce atomic operations on kmod_concurrent" considerbly.
>> > > >
>> > > > Since the sysctl interface is gone, this no longer depends on any
>> > > > other patches, the series is independent. As usual the series is
>> > > > available on my linux-next 20170526-kmod-only branch which is based
>> > > > on next-20170526.
>> > > >
>> > > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log/?h=20170526-kmod-only
>> > > >
>> > > >   Luis
>> > > >
>> > > > Luis R. Rodriguez (4):
>> > > >   module: use list_for_each_entry_rcu() on find_module_all()
>> > > >   kmod: reduce atomic operations on kmod_concurrent and simplify
>> > > >   kmod: add test driver to stress test the module loader
>> > > >   kmod: throttle kmod thread limit
>> > >
>> > > About a month now with no further nitpicks. What tree should these changes
>> > > go through if there are no issues? Andrew's, Jessica's ?
>> >
>> > Seems like going through Jessica's would make the most sense?
>>
>> Would be happy to take patches 01 (which I need to anyway), 02,
>> possibly 04 if decoupled from the test driver (03).
>
>Feel free to decouple it, but note that then the commit log must then be
>changed. My own take is this fix is not so critical as it is a corner case, so
>I have instead preferred to couple in the test case and respective fix
>together. I'll leave it up to you how to proceed.

I'll take 01 and 02 for the next merge window, as they are
straightforward. 03/04 can stay together, and as I understand it 04
may need to switch back to using the normal wait_* api.

>> I can't take patch 03 through my tree just yet, as I haven't had time to give
>> it a look yet :-/
>
>Understood. I'd appreciate at least a review though.

Of course! I should have rephrased and said *by this upcoming merge window. 

>> [ Side comment, it seems that kmod.c isn't directly maintained by anyone
>> right now, perhaps Luis would be interested in picking it up? :-) ]
>
>Sure thing, I'm not sure if it makes sense to decouple kernel/kmod.c on
>MAINTAINERS though, if you do let me know what you'd prefer to call it,
>"KMOD MODULE USERMODE HELPER" ?
>
>If you prefer to keep them together I can certainly volunteer to review all
>kmod changes and can send a patch to add kmod and myself under "MODULE
>SUPPORT".

I'm not the maintainer for kmod.c, if that's what you mean by
decoupling. But I don't think it has one, which is why I'm suggesting
adding it to MAINTAINERS, since you've been actively working on it :)
(looking at git log, it looks like Andrew did most of the sign-off's
for kmod.c in the past). I think a separate entry in MAINTAINERS is
good, with the name you suggested.

Thanks!

Jessica