linux-kernel - Re: [RFC 03/10] kmod: add dynamic max concurrent thread count

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Date:   Thu, 8 Dec 2016 22:00:40 +0100
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>, shuah@...nel.org,
        Jessica Yu <jeyu@...hat.com>,
        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>, martin.wilck@...e.com,
        Michal Marek <mmarek@...e.com>, Petr Mladek <pmladek@...e.com>,
        hare@...e.com, rwright@....com, Jeff Mahoney <jeffm@...e.com>,
        DSterba@...e.com, fdmanana@...e.com, neilb@...e.com,
        Guenter Roeck <linux@...ck-us.net>, rgoldwyn@...e.com,
        subashab@...eaurora.org, Heinrich Schuchardt <xypron.glpk@....de>,
        Aaron Tomlin <atomlin@...hat.com>, 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>,
        Andrew Morton <akpm@...ux-foundation.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: [RFC 03/10] kmod: add dynamic max concurrent thread count

On Thu, Dec 08, 2016 at 12:28:07PM -0800, Kees Cook wrote:
> On Thu, Dec 8, 2016 at 11:48 AM, Luis R. Rodriguez <mcgrof@...nel.org> wrote:
> > diff --git a/kernel/kmod.c b/kernel/kmod.c
> > index 0277d1216f80..cb6f7ca7b8a5 100644
> > --- a/kernel/kmod.c
> > +++ b/kernel/kmod.c
> > @@ -44,6 +44,9 @@
> > @@ -186,6 +174,31 @@ int __request_module(bool wait, const char *fmt, ...)
> >         return ret;
> >  }
> >  EXPORT_SYMBOL(__request_module);
> > +
> > +/*
> > + * If modprobe needs a service that is in a module, we get a recursive
> > + * loop.  Limit the number of running kmod threads to max_threads/2 or
> > + * CONFIG_MAX_KMOD_CONCURRENT, whichever is the smaller.  A cleaner method
> > + * would be to run the parents of this process, counting how many times
> > + * kmod was invoked.  That would mean accessing the internals of the
> > + * process tables to get the command line, proc_pid_cmdline is static
> > + * and it is not worth changing the proc code just to handle this case.
> > + *
> > + * "trace the ppid" is simple, but will fail if someone's
> > + * parent exits.  I think this is as good as it gets.
> > + *
> > + * You can override with with a kernel parameter, for instance to allow
> > + * 4096 concurrent modprobe instances:
> > + *
> > + *     kmod.max_modprobes=4096
> > + */
> > +void __init init_kmod_umh(void)
> 
> What does umh mean?

umh is user mode helper. kmod.c actually implements the kernel's umh code.
A subsequent series I will want to move all that to umh.c and keep module
loading separate in kmod.c But that's for later as a cleanup.

BTW any chance I can have you trim replies to file name and hunk for changes
you reply to ? As an example I did that here :)

  Luis