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

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Date:	Wed, 11 Feb 2009 13:27:19 -0800
From:	akpm@...ux-foundation.org
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, akpm@...ux-foundation.org,
	andi@...stfloor.org
Subject: [patch 1/2] net: don't use in_atomic() in gfp_any()

From: Andrew Morton <akpm@...ux-foundation.org>

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.

Cc: Andi Kleen <andi@...stfloor.org>
Cc: "David S. Miller" <davem@...emloft.net>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

 include/net/sock.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN include/net/sock.h~net-dont-use-in_atomic-in-gfp_any include/net/sock.h
--- a/include/net/sock.h~net-dont-use-in_atomic-in-gfp_any
+++ a/include/net/sock.h
@@ -1313,7 +1313,7 @@ static inline int sock_writeable(const s

 static inline gfp_t gfp_any(void)
 {
-	return in_atomic() ? GFP_ATOMIC : GFP_KERNEL;
+	return in_softirq() ? GFP_ATOMIC : GFP_KERNEL;
 }

 static inline long sock_rcvtimeo(const struct sock *sk, int noblock)
_
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