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From: Cong Wang <xiyou.wangcong@gmail.com>
To: Girish Moodalbail <girish.moodalbail@oracle.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
	Alexander Duyck <alexander.duyck@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
	Network Development <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	intel-wired-lan <intel-wired-lan@lists.osuosl.org>
Subject: Re: [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf
Date: Thu, 9 Nov 2017 16:16:01 -0800	[thread overview]
Message-ID: <CAM_iQpUBDHkrC4kirFdM6ff==9dot5+q+8L_fx2vfRLq+2+Zqw@mail.gmail.com> (raw)
In-Reply-To: <008a7e8d-86e2-0709-d2ae-8aa743ef12ac@oracle.com>

On Thu, Nov 9, 2017 at 7:51 AM, Girish Moodalbail
<girish.moodalbail@oracle.com> wrote:
>
> Upon receiving NETDEV_DOWN event, we are calling
>
>         vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
>
> which in turn calls call_rcu() to queue vlan_info_free_rcu() to be called at
> some point. This free function frees the array[]
> (vlan_info.vlan_grp.vn_devices_array).  My guess is that
> vlan_info_free_rcu() is being called first and then the array[] is being
> accessed in vlan_device_event().
>

Well yes and no.

No, RCU itself is not broken and we clearly unpublish the RCU pointer
before calling call_rcu().

Yes, I see where it is broken: the grp pointer still points to old
dev->vlan_info, we should re-fetch it after vlan_vid_del().

I will send a fix.

Thanks!

WARNING: multiple messages have this Message-ID (diff)
From: Cong Wang <xiyou.wangcong@gmail.com>
To: intel-wired-lan@osuosl.org
Subject: [Intel-wired-lan] [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf
Date: Thu, 9 Nov 2017 16:16:01 -0800	[thread overview]
Message-ID: <CAM_iQpUBDHkrC4kirFdM6ff==9dot5+q+8L_fx2vfRLq+2+Zqw@mail.gmail.com> (raw)
In-Reply-To: <008a7e8d-86e2-0709-d2ae-8aa743ef12ac@oracle.com>

On Thu, Nov 9, 2017 at 7:51 AM, Girish Moodalbail
<girish.moodalbail@oracle.com> wrote:
>
> Upon receiving NETDEV_DOWN event, we are calling
>
>         vlan_vid_del(dev, htons(ETH_P_8021Q), 0);
>
> which in turn calls call_rcu() to queue vlan_info_free_rcu() to be called at
> some point. This free function frees the array[]
> (vlan_info.vlan_grp.vn_devices_array).  My guess is that
> vlan_info_free_rcu() is being called first and then the array[] is being
> accessed in vlan_device_event().
>

Well yes and no.

No, RCU itself is not broken and we clearly unpublish the RCU pointer
before calling call_rcu().

Yes, I see where it is broken: the grp pointer still points to old
dev->vlan_info, we should re-fetch it after vlan_vid_del().

I will send a fix.

Thanks!

  reply	other threads:[~2017-11-10  0:16 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-07 10:21 [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf Fengguang Wu
2017-11-07 16:25 ` Linus Torvalds
2017-11-07 16:46   ` Fengguang Wu
2017-11-08  9:48   ` Fengguang Wu
2017-11-08 16:20     ` Linus Torvalds
2017-11-08 16:20       ` [Intel-wired-lan] " Linus Torvalds
2017-11-08 17:12       ` Fengguang Wu
2017-11-08 17:12         ` [Intel-wired-lan] " Fengguang Wu
2017-11-08 17:18         ` Fengguang Wu
2017-11-08 17:18           ` [Intel-wired-lan] " Fengguang Wu
2017-11-08 18:05         ` Linus Torvalds
2017-11-08 18:05           ` [Intel-wired-lan] " Linus Torvalds
2017-11-08 18:36         ` Alexander Duyck
2017-11-08 18:36           ` [Intel-wired-lan] " Alexander Duyck
2017-11-09  3:12           ` Fengguang Wu
2017-11-09  3:12             ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  4:09             ` Fengguang Wu
2017-11-09  4:09               ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  7:22               ` Fengguang Wu
2017-11-09  7:22                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  6:34             ` Cong Wang
2017-11-09  6:34               ` [Intel-wired-lan] " Cong Wang
2017-11-09  6:55               ` Fengguang Wu
2017-11-09  6:55                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  7:43                 ` Fengguang Wu
2017-11-09  7:43                   ` [Intel-wired-lan] " Fengguang Wu
2017-11-09 15:51               ` Girish Moodalbail
2017-11-09 15:51                 ` [Intel-wired-lan] " Girish Moodalbail
2017-11-10  0:16                 ` Cong Wang [this message]
2017-11-10  0:16                   ` Cong Wang
2017-11-12 19:31         ` Linus Torvalds
2017-11-12 19:31           ` [Intel-wired-lan] " Linus Torvalds
2017-11-13  1:13           ` CONFIG_DEBUG_INFO_SPLIT impacts on faddr2line Fengguang Wu
2017-11-13  1:13             ` [Intel-wired-lan] " Fengguang Wu
2017-11-13  2:05             ` Zhang Rui
2017-11-13  2:05               ` [Intel-wired-lan] " Zhang Rui
2017-11-13  2:22               ` Fengguang Wu
2017-11-13  2:22                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-13 18:52             ` Andi Kleen
2017-11-13 18:52               ` [Intel-wired-lan] " Andi Kleen
2017-11-13 19:14               ` Linus Torvalds
2017-11-13 19:14                 ` [Intel-wired-lan] " Linus Torvalds
2017-11-13 20:10                 ` Andi Kleen
2017-11-13 20:10                   ` [Intel-wired-lan] " Andi Kleen
2017-11-13 20:14                   ` H.J. Lu
2017-11-13 20:14                     ` [Intel-wired-lan] " H.J. Lu
2017-11-13 20:56                   ` Linus Torvalds
2017-11-13 20:56                     ` [Intel-wired-lan] " Linus Torvalds
2017-11-13 21:41                     ` Andi Kleen
2017-11-13 21:41                       ` [Intel-wired-lan] " Andi Kleen
2017-11-13 21:57                       ` Linus Torvalds
2017-11-13 21:57                         ` [Intel-wired-lan] " Linus Torvalds
2017-11-13 23:51                         ` Andi Kleen
2017-11-13 23:51                           ` [Intel-wired-lan] " Andi Kleen
2017-11-14  8:13               ` Fengguang Wu
2017-11-14  8:13                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  2:43     ` [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf Fengguang Wu
2017-11-09  6:48       ` Fengguang Wu

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