netdev - Re: [PATCH net] inet: frag: make sure forced eviction removes all frags

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Date:	Thu, 06 Mar 2014 09:36:22 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Westphal <fw@...len.de>
Cc:	netdev@...r.kernel.org, Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH net] inet: frag: make sure forced eviction removes all
 frags

On Thu, 2014-03-06 at 18:06 +0100, Florian Westphal wrote:
> Quoting Alexander Aring:
>   While fragmentation and unloading of 6lowpan module I got this kernel Oops
>   after few seconds:
> 
>   BUG: unable to handle kernel paging request at f88bbc30
>   [..]
>   Modules linked in: ipv6 [last unloaded: 6lowpan]
>   Call Trace:
>    [<c012af4c>] ? call_timer_fn+0x54/0xb3
>    [<c012aef8>] ? process_timeout+0xa/0xa
>    [<c012b66b>] run_timer_softirq+0x140/0x15f
> 
> Problem is that incomplete frags are still around after unload; when
> their frag expire timer fires, we get crash.
> 
> When a netns is removed (also done when unloading module), inet_frag
> calls the evictor with 'force' argument to purge remaining frags.
> 
> The evictor loop terminates when accounted memory ('work') drops to 0
> or the lru-list becomes empty.  However, the mem accounting is done
> via percpu counters and may not be accurate, i.e. loop may terminate
> prematurely.
> 
> Alter evictor to only stop once the lru list is empty when force is
> requested.
> 
> Reported-by: Phoebe Buckheister <phoebe.buckheister@...m.fraunhofer.de>
> Reported-by: Alexander Aring <alex.aring@...il.com>
> Tested-by: Alexander Aring <alex.aring@...il.com>
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
> 
> diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
> index 322dceb..3b01959 100644
> --- a/net/ipv4/inet_fragment.c
> +++ b/net/ipv4/inet_fragment.c
> @@ -208,7 +208,7 @@ int inet_frag_evictor(struct netns_frags *nf, struct inet_frags *f, bool force)
>  	}
>  
>  	work = frag_mem_limit(nf) - nf->low_thresh;
> -	while (work > 0) {
> +	while (work > 0 || force) {
>  		spin_lock(&nf->lru_lock);
>  
>  		if (list_empty(&nf->lru_list)) {

Fixes: 6d7b857d541e ("net: use lib/percpu_counter API for fragmentation mem accounting")
Cc: Jesper Dangaard Brouer <brouer@...hat.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>



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