linux-kernel - Re: [PATCH] sdhci: Fix potential spinlock recursion

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Date:	Thu, 15 Jan 2009 17:32:57 +0300
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Pierre Ossman <drzeus@...eus.cx>
Cc:	sdhci-devel@...t.drzeus.cx, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sdhci: Fix potential spinlock recursion

On Thu, Jan 15, 2009 at 07:05:21AM +0100, Pierre Ossman wrote:
> On Wed, 14 Jan 2009 22:41:59 +0300
> Anton Vorontsov <avorontsov@...mvista.com> wrote:
> 
> > 
> > This happens because plain spin_lock() won't protect us from
> > softirqs (tasklets). So in the sdhci interrupt handler we must
> > grab the _irq version of the lock.
> > 
> 
> ?! The docs I've read state that softirq:s are not executed until all
> the hardirq:s have finished processing. And looking at your code, that
> seems to still hold true. A softirq running esdhc_tasklet_card() gets
> preempted by a hard irq and we have the lockup.

Right you are. That was a total brain fart on my part, I apologize.

> If you're running the code you sent a few minutes later, then something
> is broken with your platform as esdhc_tasklet_card() clearly tries to
> disable interrupts when it grabs the lock.

Luckily the platform isn't broken. It's just that sdhci driver
doesn't have this bug, I was a bit confused by two these drivers
instead.

Here is the original patch that has this bug:

http://www.bitshrine.org/gpp/kernel-2.6.25-MPC837xE-RDB-add-esdhc-support.patch

Notice that esdhc_tasklet_card() grabs spin_lock(), not
spin_lock_irqsave() as sdhci driver. I fixed this in the esdhc patch
that I sent, but then I decided to "fix" irq handler too, which
wasn't necessary, of course. And that's it.

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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