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

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Date:	Wed, 02 Sep 2009 23:10:17 -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: 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!
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