netdev - Re: [PATCH 6/6] net: Free skbs from irqs when possible.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 18 Mar 2014 08:23:58 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	David Miller <davem@...emloft.net>, eric.dumazet@...il.com,
	netdev@...r.kernel.org, xiyou.wangcong@...il.com, mpm@...enic.com,
	satyam.sharma@...il.com
Subject: Re: [PATCH 6/6] net: Free skbs from irqs when possible.

On Mon, 17 Mar 2014 23:27:52 -0700
ebiederm@...ssion.com (Eric W. Biederman) wrote:

> Add a test skb_irq_freeable to report when it is safe to free a skb
> from irq context.
> 
> It is not safe to free an skb from irq context when:
> - The skb has a destructor as some skb destructors call local_bh_disable
>   or spin_lock_bh.
> - There is xfrm state as __xfrm_state_destroy calls spin_lock_bh.
> - There is netfilter conntrack state as destroy_conntrack calls
>   spin_lock_bh.
> - If there is a refcounted dst entry on the skb, as __dst_free
>   calls spin_lock_bh.
> - If there is a frag_list, which could be a list of any skbs.
> Otherwise it appears safe to free a skb from interrupt context.
> 
> - Update the warning in skb_releae_head_state to warn about freeing
>   skb's in the wrong context.
> 
> - Update __dev_kfree_skb_irq to free all skbs that it can immediately
> 
> - Kill zap_completion_queue because there is no point going through
>   a queue of packets that are not safe to free and looking for packets
>   that are safe to free.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>

Why introduce the additional complexity for so little gain?
It looks like you are only optimizing for the corner case where netpoll
is cleaning up on Tx.

-1
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html