netdev - Re: [patch 1/2] net: don't use in_atomic() in gfp

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Message-Id: <20090212.164330.59402005.davem@davemloft.net>
Date:	Thu, 12 Feb 2009 16:43:30 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	akpm@...ux-foundation.org
Cc:	netdev@...r.kernel.org, andi@...stfloor.org
Subject: Re: [patch 1/2] net: don't use in_atomic() in gfp_any()

From: akpm@...ux-foundation.org
Date: Wed, 11 Feb 2009 13:27:19 -0800

> The problem is that in_atomic() will return false inside spinlocks if
> CONFIG_PREEMPT=n.  This will lead to deadlockable GFP_KERNEL allocations
> from spinlocked regions.
> 
> Secondly, if CONFIG_PREEMPT=y, this bug solves itself because networking
> will instead use GFP_ATOMIC from this callsite.  Hence we won't get the
> might_sleep() debugging warnings which would have informed us of the buggy
> callsites.
> 
> Solve both these problems by switching to in_interrupt().  Now, if someone
> runs a gfp_any() allocation from inside spinlock we will get the warning
> if CONFIG_PREEMPT=y.
> 
> I reviewed all callsites and most of them were too complex for my little
> brain and none of them documented their interface requirements.  I have no
> idea what this patch will do.
> 
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Applied.
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