netdev - Re: __napi_alloc_skb failures locking up the box

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Date:	Sat, 30 Apr 2016 12:54:12 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Aaro Koskinen <aaro.koskinen@....fi>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: __napi_alloc_skb failures locking up the box

On Sat, 2016-04-30 at 22:24 +0300, Aaro Koskinen wrote:
> Hi,
> 
> I have old NAS box (Thecus N2100) with 512 MB RAM, where rsync from NFS ->
> disk reliably results in temporary out-of-memory conditions.
> 
> When this happens the dmesg gets flooded with below logs. If the serial
> console logging is enabled, this will lock up the box completely and
> the backup is not making any progress.
> 
> Shouldn't these allocation failures be ratelimited somehow (or even made
> silent)? It doesn't sound right if I can lock up the system simply by
> copying files...

Agreed.

All napi_alloc_skb() callers handle failure just fine.

If they did not, a NULL deref would produce a proper stack dump.

When memory gets this tight, other traces will be dumped anyway.

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 15d0df943466..0652709fe81a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2423,7 +2423,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
 static inline struct sk_buff *napi_alloc_skb(struct napi_struct *napi,
 					     unsigned int length)
 {
-	return __napi_alloc_skb(napi, length, GFP_ATOMIC);
+	return __napi_alloc_skb(napi, length, GFP_ATOMIC | __GFP_NOWARN);
 }
 void napi_consume_skb(struct sk_buff *skb, int budget);