From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH 3/3] net: skb_queue_purge(): lock/unlock the list only once Date: Fri, 08 Sep 2017 09:01:19 -0700 Message-ID: <1504886479.15310.74.camel@edumazet-glaptop3.roam.corp.google.com> References: <45aab5effc0c424a992646a97cf2ec14-mfwitten@gmail.com> <60c8906b751d4915be456009c220516e-mfwitten@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Michael Witten Return-path: In-Reply-To: <60c8906b751d4915be456009c220516e-mfwitten@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, 2017-09-08 at 05:06 +0000, Michael Witten wrote: > Date: Thu, 7 Sep 2017 20:07:40 +0000 > With this commit, the list's lock is locked/unlocked only once > for the duration of `skb_queue_purge()'. > > Hitherto, the list's lock has been locked/unlocked every time > an item is dequeued; this seems not only inefficient, but also > incorrect, as the whole point of `skb_queue_purge()' is to clear > the list, presumably without giving anything else a chance to > manipulate the list in the interim. > > Signed-off-by: Michael Witten > --- > net/core/skbuff.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 68065d7d383f..66c0731a2a5f 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -2834,9 +2834,13 @@ EXPORT_SYMBOL(skb_dequeue_tail); > */ > void skb_queue_purge(struct sk_buff_head *list) > { > + unsigned long flags; > struct sk_buff *skb; > - while ((skb = skb_dequeue(list)) != NULL) > + > + spin_lock_irqsave(&list->lock, flags); > + while ((skb = __skb_dequeue(list)) != NULL) > kfree_skb(skb); > + spin_unlock_irqrestore(&list->lock, flags); > } > EXPORT_SYMBOL(skb_queue_purge); > No, this is very wrong : Holding hard IRQ for a potential very long time is going to break horribly. Some lists can have 10,000+ skbs in them. Note that net-next tree is currently closed, please read Documentation/networking/netdev-FAQ.txt