netdev - Re: segfault after VLAN change

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Message-ID: <87simk1bhu.fsf@nemi.mork.no>
Date:	Wed, 02 Jul 2014 09:11:09 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	Madalin-Cristian Bucur <madalin.bucur@...escale.com>
Cc:	Li RongQing <roy.qing.li@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	"netdev\@vger.kernel.org" <netdev@...r.kernel.org>
Subject: Re: segfault after VLAN change

Madalin-Cristian Bucur <madalin.bucur@...escale.com> writes:

> Hello,
>
> I've discovered that the commit:
>
>     commit 5a4ae5f6e7d4b2b5a9b8981d513345053e40b6ac
>     Author: Li RongQing <roy.qing.li@...il.com>
>     Date:   Mon Apr 21 19:49:08 2014 +0800
>
>     vlan: unnecessary to check if vlan_pcpu_stats is NULL
>
>     if allocating memory for vlan_pcpu_stats failed, the device can not be operated
>
>     Signed-off-by: 
>     Cc: Eric Dumazet <edumazet@...gle.com>
>     Signed-off-by: David S. Miller <davem@...emloft.net>
>
> is causing a segfault when removing vlan on a e1000 device (reproduces with other devices as well).
> Re-adding the check or reverting the patch removes the issue (log below).


Yes, that commit should be reverted.

The commit message makes it clear that only allocation failures were
considered, while a simple grep reveals that there at least one site
where that field is explicitly NULLed:

bjorn@...i:/usr/local/src/git/linux$ git grep vlan_pcpu_stats net/8021q/
net/8021q/vlan_core.c:  struct vlan_pcpu_stats *rx_stats;
net/8021q/vlan_core.c:  rx_stats = this_cpu_ptr(vlan_dev_priv(vlan_dev)->vlan_pcpu_stats);
net/8021q/vlan_dev.c:           struct vlan_pcpu_stats *stats;
net/8021q/vlan_dev.c:           stats = this_cpu_ptr(vlan->vlan_pcpu_stats);
net/8021q/vlan_dev.c:           this_cpu_inc(vlan->vlan_pcpu_stats->tx_dropped);
net/8021q/vlan_dev.c:   vlan_dev_priv(dev)->vlan_pcpu_stats = netdev_alloc_pcpu_stats(struct vlan_pcpu_stats);
net/8021q/vlan_dev.c:   if (!vlan_dev_priv(dev)->vlan_pcpu_stats)
net/8021q/vlan_dev.c:   free_percpu(vlan->vlan_pcpu_stats);
net/8021q/vlan_dev.c:   vlan->vlan_pcpu_stats = NULL;
net/8021q/vlan_dev.c:   struct vlan_pcpu_stats *p;
net/8021q/vlan_dev.c:           p = per_cpu_ptr(vlan_dev_priv(dev)->vlan_pcpu_stats, i);


Without looking further it seems likely that this is done during
teardown, making the original NULL check necessary.



Bjørn
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