Re: [PATCH] firmware: wake all waiters

From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	"Luis R. Rodriguez" <mcgrof@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	DanielWagnerwagi@monom.org, Boqun Feng <boqun.feng@gmail.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Paul Gortmaker <paul.gortmaker@windriver.com>,
	Ming Lei <ming.lei@redhat.com>, "Li, Yi" <yi1.li@linux.intel.com>,
	"AKASHI, Takahiro" <takahiro.akashi@linaro.org>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Petr Mladek <pmladek@suse.com>,
	Andrew Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	David Howells <dhowells@redhat.com>,
	Alan Cox <alan@linux.intel.com>, "Theodore Ts'o" <tytso@mit.edu>,
	oss-drivers@netronome.com
Subject: Re: [PATCH] firmware: wake all waiters
Date: Wed, 12 Jul 2017 20:45:19 +0200	[thread overview]
Message-ID: <20170712184519.GV21846@wotan.suse.de> (raw)
In-Reply-To: <CA+55aFwwyx61OdiZA0KF4Hs68D6SKO5m7vdru_z=Qh3pPnr6Dw@mail.gmail.com>

On Wed, Jul 05, 2017 at 09:33:38AM -0700, Linus Torvalds wrote:
> On Wed, Jul 5, 2017 at 9:18 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > In any case, I'm not seeing why you call it idiotic.
> 
> Have you read the problems?
> 
> There were originally three users:
> 
>  - one of them is firmware loading, and it was actively *buggy* due to
> using hat shit interface, and it's going away

To be fair the issue with the firmware loading was due to a regression on the
port from using swait/completion to swait. swake_up() was used instead of
swake_up_all(). Before the port complate_all() was used instead of just
complete().

So I would personally not add the firmware API to the list of reasons why swait
would be crap.

The more *general* semantics issue you pointed out with swake_up() though seem
more reasonable to be attacking the swait API and those are best followed on
the other thread [0].

I should also point out that there are *other* issues with the firmware API on
this whole wait stuff, but that have been present since even before when we
were using the regular wait / completion API -- a wake was never issued upon an
error in some situations on some kernel builds. I have a fix for that now along
with a test case for it which I'll post soon. After all these fixes the code
works as expected with either the swait API or the good 'ol wait/completion
API. But given swait is still out by you as only specialized I did already post
patches to revert the firmware API to switch back to the wait/completion API.

[0] https://lkml.kernel.org/r/CA+55aFykNULx-b6M6FmUYdK2cn-OJKKfjaPwLN5xZGK+bioGaA@mail.gmail.com

  Luis