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

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Date:	Wed, 09 May 2007 16:35:06 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Pierre Ossman <drzeus-list@...eus.cx>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] MMC updates

Pierre Ossman wrote:
> Nick Piggin wrote:
> 
>>>@@ -501,9 +501,9 @@ void mmc_detect_change(struct mmc_host *host,
>>>unsigned long delay)
>>> {
>>> #ifdef CONFIG_MMC_DEBUG
>>>     unsigned long flags;
>>>-    spin_lock_irqsave(host->lock, flags);
>>>+    spin_lock_irqsave(&host->lock, flags);
>>>     BUG_ON(host->removed);
>>>-    spin_unlock_irqrestore(host->lock, flags);
>>>+    spin_unlock_irqrestore(&host->lock, flags);
>>> #endif
>>
>>Do you actually need the lock there at all? What is it protecting?
>>
> 
> 
> It makes sure we don't have any race when it comes to modifying
> host->removed.

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.

-- 
SUSE Labs, Novell Inc.
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