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From: Greg KH on 30 Mar 2010 20:50
2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Robert Varga <nite(a)hq.alert.sk>

commit 657e9649e745b06675aa5063c84430986cdc3afa upstream.

I have recently came across a preemption imbalance detected by:

<4>huh, entered ffffffff80644630 with preempt_count 00000102, exited with 00000101?
<0>------------[ cut here ]------------
<2>kernel BUG at /usr/src/linux/kernel/timer.c:664!
<0>invalid opcode: 0000 [1] PREEMPT SMP

with ffffffff80644630 being inet_twdr_hangman().

This appeared after I enabled CONFIG_TCP_MD5SIG and played with it a
bit, so I looked at what might have caused it.

One thing that struck me as strange is tcp_twsk_destructor(), as it
calls tcp_put_md5sig_pool() -- which entails a put_cpu(), causing the
detected imbalance. Found on 2.6.23.9, but 2.6.31 is affected as well,
as far as I can tell.

Signed-off-by: Robert Varga <nite(a)hq.alert.sk>
Signed-off-by: David S. Miller <davem(a)davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
net/ipv4/tcp_minisocks.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -362,7 +362,7 @@ void tcp_twsk_destructor(struct sock *sk
#ifdef CONFIG_TCP_MD5SIG
struct tcp_timewait_sock *twsk = tcp_twsk(sk);
if (twsk->tw_md5_keylen)
- tcp_put_md5sig_pool();
+ tcp_free_md5sig_pool();
#endif
}



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