netdev - Re: [PATCH net] tcp: fix possible deadlock in tcp_send

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Date:	Wed, 22 Apr 2015 14:15:34 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	johunt@...mai.com, netdev@...r.kernel.org, edumazet@...gle.com,
	gthelen@...gle.com, rientjes@...gle.com
Subject: Re: [PATCH net] tcp: fix possible deadlock in tcp_send_fin()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 21 Apr 2015 18:32:24 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Using sk_stream_alloc_skb() in tcp_send_fin() is dangerous in
> case a huge process is killed by OOM, and tcp_mem[2] is hit.
> 
> To be able to free memory we need to make progress, so this
> patch allows FIN packets to not care about tcp_mem[2], if
> skb allocation succeeded.
> 
> In a follow-up patch, we might abort tcp_send_fin() infinite loop
> in case TIF_MEMDIE is set on this thread, as memory allocator
> did its best getting extra memory already. 
> 
> This patch reverts d22e15371811 ("tcp: fix tcp fin memory accounting")
> 
> Fixes: d22e15371811 ("tcp: fix tcp fin memory accounting")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable, since the tcp fin memory accounting change
went to -stable already.

Wrt. longer term solutions, I would even be OK at this point aborting
the connection altogether if the skb allocation fails period.  Not
just if TIF_MEMDIE is set.  That endless loop has been nothing but
trouble.

Thanks.
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