linux-kernel - Re: [GIT PULL] MMC updates

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Date:	Wed, 09 May 2007 09:51:51 +0200
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] MMC updates

Nick Piggin wrote:
>
> If you want to ensure you always only modify host->removed from under
> the spinlock, it would be enforcable by introducing an accessor function
> and doing a BUG_ON(!spin_is_locked()) in there.
>
> If you just want to ensure that host->removed is 0 at this point, you
> shouldn't need any spinlocks AFAIKS... that way you can probably afford
> to move it out from CONFIG_MMC_DEBUG and get wider testing.
>

The host->removed member is only used for this simple test. It is set in
mmc_host_remove() to indicate that the removal process has begun. At
this point it is invalid to call mmc_detect_change() (the place this
patch fixes). So the spinlocks are mostly there so that things are
properly ordered when we go SMP. Some creative barriers would probably
work as well, but I find spinlocks more "normal" and hence more readable.

Rgds

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org

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