Re: [PATCH] RFC: mmc: block: replace semaphore with freezing

From: Arnd Bergmann <arnd@arndb.de>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Chunyan Zhang <zhang.chunyan@linaro.org>,
	Baolin Wang <baolin.wang@linaro.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	Russell King <linux@armlinux.org.uk>,
	Jiri Kosina <jikos@kernel.org>
Subject: Re: [PATCH] RFC: mmc: block: replace semaphore with freezing
Date: Wed, 16 Nov 2016 17:32:44 +0100	[thread overview]
Message-ID: <17679227.zg8zl3jhbr@wuerfel> (raw)
In-Reply-To: <CACRpkdY+jdU4ETuMJsY-efSkjwE0fWWRZoyCyrYAs_GxUo-DhQ@mail.gmail.com>

On Wednesday, November 16, 2016 4:20:47 PM CET Linus Walleij wrote:
> On Wed, Nov 16, 2016 at 1:46 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> 
> > Well, we had a session at the KS regarding usage of the freezer on
> > kernel threads and the conclusion was to get rid of that (as opposed
> > to freezing user space, which is necessary IMO).  So this change would
> > go in the opposite direction. 
> 
> Aha so I should not make this thread look like everyone else, instead
> everyone else should look like this thread, haha 
> 
> Ah well, I'll just drop it.

It would still be good to remove the semaphore and do something else,
as we also want to remove all semaphores. ;-)

We could check "mq->flags & MMC_QUEUE_SUSPENDED" in the kthread to see
if the queue is currently suspended, and otherwise go to sleep there,
and then call wake_up() in the resume function.

While looking at that code, I just noticed that access to 
mq->flags is racy and should be fixed as well.

	Arnd