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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Fri, 23 Aug 2019 15:42:47 +0200
Message-ID: <CAKMK7uHzSkd2j4MvSMoHhCaSE0BT0zMo9osF4FUBYwNZrVfYDA@mail.gmail.com>
Subject: Re: [PATCH 3/4] kernel.h: Add non_block_start/end()
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        DRI Development <dri-devel@lists.freedesktop.org>,
        Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Michal Hocko <mhocko@suse.com>,
        David Rientjes <rientjes@google.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Wei Wang <wvw@google.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jann Horn <jannh@google.com>, Feng Tang <feng.tang@intel.com>,
        Kees Cook <keescook@chromium.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Daniel Vetter <daniel.vetter@intel.com>
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On Fri, Aug 23, 2019 at 2:12 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Fri, Aug 23, 2019 at 10:34:01AM +0200, Daniel Vetter wrote:
> > On Fri, Aug 23, 2019 at 1:14 AM Andrew Morton <akpm@linux-foundation.org> wrote:
> > >
> > > On Tue, 20 Aug 2019 22:24:40 +0200 Daniel Vetter <daniel@ffwll.ch> wrote:
> > >
> > > > Hi Peter,
> > > >
> > > > Iirc you've been involved at least somewhat in discussing this. -mm folks
> > > > are a bit undecided whether these new non_block semantics are a good idea.
> > > > Michal Hocko still is in support, but Andrew Morton and Jason Gunthorpe
> > > > are less enthusiastic. Jason said he's ok with merging the hmm side of
> > > > this if scheduler folks ack. If not, then I'll respin with the
> > > > preempt_disable/enable instead like in v1.
> > >
> > > I became mollified once Michel explained the rationale.  I think it's
> > > OK.  It's very specific to the oom reaper and hopefully won't be used
> > > more widely(?).
> >
> > Yeah, no plans for that from me. And I hope the comment above them now
> > explains why they exist, so people think twice before using it in
> > random places.
>
> I still haven't heard a satisfactory answer why a whole new scheme is
> needed and a simple:
>
>    if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP))
>         preempt_disable()
>
> isn't sufficient to catch the problematic cases during debugging??
> IMHO the fact preempt is changed by the above when debugging is not
> material here. I think that information should be included in the
> commit message at least.
>
> But if sched people are happy then lets go ahead. Can you send a v2
> with the check encompassing the invalidate_range_end?

Yes I will resend with this patch plus the next, amended as we
discussed, plus the might_sleep annotations. I'm assuming the lockdep
one will land, so not going to resend that.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch