linux-kernel - Re: [PATCH] kthread: finer-grained lockdep/cross-release completion

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Message-ID: <20171219095925.GY26573@phenom.ffwll.local>
Date:   Tue, 19 Dec 2017 10:59:25 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Marta Lofstedt <marta.lofstedt@...el.com>,
        Byungchul Park <byungchul.park@....com>,
        Ingo Molnar <mingo@...nel.org>, Tejun Heo <tj@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>, Shaohua Li <shli@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] kthread: finer-grained lockdep/cross-release completion

On Mon, Dec 18, 2017 at 09:42:13AM -0800, Linus Torvalds wrote:
> On Sun, Dec 17, 2017 at 11:11 PM, Daniel Vetter <daniel@...ll.ch> wrote:
> >
> > This didn't seem to have made it into -rc4. Anything needed to get it
> > going?
> 
> Do you actually see the problem in -rc4?
> 
> Because we ended up removing the cross-release checking due to other
> developers complaining. It seemed to need a lot more work before it
> was ready.
> 
> So I suspect the patch is simply not relevant any more (even if it's
> not necessarily wrong either).

Awww ... I like the cross release stuff, it's catching lots of good bugs
for us - writing a gpu memory manager that's supposed to interface with
the core one ain't the simplest thing to get right. That's also why we're
going around and fixing up fallout (we've worked on the worker annotations
for 4.14 too). I guess next release, hopefully.

I think between 4.14 and 4.15 attemps cross-release spotted around 5 or so
genuine deadlocks in i915 code. And at least right now, with the current
set of fixups our CI runs are splat-free. So at least a Kconfig option
would be nice, to be able to enable it easily when you want to.

Wrt us not noticing: Getting the patches in through normal means takes too
long, so we constantly carry arounda  bunch of fixup patches to address
serious issues that block CI (no lockdep is no good CI). That's why we
won't immediately notice when an issue is resolved some other way.

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch