linux-kernel - Regression in staging:r8712u since 3.4 merge

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Message-ID: <50119697.5050807@lwfinger.net>
Date:	Thu, 26 Jul 2012 14:12:23 -0500
From:	Larry Finger <Larry.Finger@...inger.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Neal Cardwell <ncardwell@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Regression in staging:r8712u since 3.4 merge

Since kernel 3.4, driver r8712u has yielded intermittent errors when connected 
to a secure connection. With Firefox, the message is "Secure Connection Failed: 
SSL received a record with an incorrect Message Authentication Code (Error code: 
ssl_error_bad_mac_read)". A retry may work eventually, When using wget with an 
https URL, the error message is "SSL3_GET_RECORD: decryption failed or bad 
record mac".

This regression is the basis for https://bugzilla.kernel.org/show_bug.cgi?id=45071.

Although intermittent, I managed to bisect the problem. The bad commit is

==========================================================================
commit c8628155ece363487b57d33441ea0359018c0fa7
Author: Eric Dumazet <eric.dumazet@...il.com>
Date:   Sun Mar 18 11:07:47 2012 +0000

     tcp: reduce out_of_order memory use

     With increasing receive window sizes, but speed of light not improved
     that much, out of order queue can contain a huge number of skbs, waiting
     to be moved to receive_queue when missing packets can fill the holes.

     Some devices happen to use fat skbs (truesize of 4096 + sizeof(struct
     sk_buff)) to store regular (MTU <= 1500) frames. This makes highly
     probable sk_rmem_alloc hits sk_rcvbuf limit, which can be 4Mbytes in
     many cases.

     When limit is hit, tcp stack calls tcp_collapse_ofo_queue(), a true
     latency killer and cpu cache blower.

     Doing the coalescing attempt each time we add a frame in ofo queue
     permits to keep memory use tight and in many cases avoid the
     tcp_collapse() thing later.

     Tested on various wireless setups (b43, ath9k, ...) known to use big skb
     truesize, this patch removed the "packets collapsed in receive queue due
     to low socket buffer" I had before.

     This also reduced average memory used by tcp sockets.

     With help from Neal Cardwell.

     Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
     Cc: Neal Cardwell <ncardwell@...gle.com>
     Cc: Yuchung Cheng <ycheng@...gle.com>
     Cc: H.K. Jerry Chu <hkchu@...gle.com>
     Cc: Tom Herbert <therbert@...gle.com>
     Cc: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
     Acked-by: Neal Cardwell <ncardwell@...gle.com>
     Signed-off-by: David S. Miller <davem@...emloft.net>
============================================================================

As every other network driver is OK with this patch, I know the problem is in 
r8712u. Do you have any thoughts on what it might be doing wrong to cause this 
problem?

Thanks,

Larry

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