netdev - Re: [PATCH][RESEND] tcp: replace hard coded GFP_KERNEL with sk

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Message-Id: <20090902.233225.203837229.davem@davemloft.net>
Date:	Wed, 02 Sep 2009 23:32:25 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	fengguang.wu@...el.com
Cc:	herbert@...dor.apana.org.au, acme@...stprotocols.net,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH][RESEND] tcp: replace hard coded GFP_KERNEL with
 sk_allocation

From: David Miller <davem@...emloft.net>
Date: Wed, 02 Sep 2009 23:10:17 -0700 (PDT)

> From: Wu Fengguang <fengguang.wu@...el.com>
> Date: Thu, 3 Sep 2009 12:04:07 +0800
> 
>> This fixed a lockdep warning which appeared when doing stress
>> memory tests over NFS:
>> 
>> 	inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
>> 
>> 	page reclaim => nfs_writepage => tcp_sendmsg => lock sk_lock
>> 
>> 	mount_root => nfs_root_data => tcp_close => lock sk_lock =>
>> 			tcp_send_fin => alloc_skb_fclone => page reclaim
>> 
>> David raised a concern that if the allocation fails in tcp_send_fin(), and it's
>> GFP_ATOMIC, we are going to yield() (which sleeps) and loop endlessly waiting
>> for the allocation to succeed.
>> 
>> But fact is, the original GFP_KERNEL also sleeps. GFP_ATOMIC+yield() looks
>> weird, but it is no worse the implicit sleep inside GFP_KERNEL. Both could
>> loop endlessly under memory pressure.
>> 
>> CC: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
>> CC: David S. Miller <davem@...emloft.net>
>> CC: Herbert Xu <herbert@...dor.apana.org.au>
>> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> 
> Applied to net-next-2.6, thanks!

You obviously didn't build test this with TCP MD5 support
enabled, that fails.

I'm fixing it up, but if you're going to go through the motions
of submitting a patch multiple times, at least do a thorough
build test of the code you're changing.
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