netdev - RE: [PATCH net V3 2/2] tuntap: synchronize through tfiles array instead of tun->numqueues

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Date:   Thu, 9 May 2019 11:42:36 +0000
From:   "weiyongjun (A)" <weiyongjun1@...wei.com>
To:     Jason Wang <jasowang@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     yuehaibing <yuehaibing@...wei.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "eric.dumazet@...il.com" <eric.dumazet@...il.com>
Subject: RE: [PATCH net V3 2/2] tuntap: synchronize through tfiles array
 instead of tun->numqueues

> -----Original Message-----
> From: Jason Wang [mailto:jasowang@...hat.com]
> Sent: Thursday, May 09, 2019 11:20 AM
> To: netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> Cc: yuehaibing <yuehaibing@...wei.com>; xiyou.wangcong@...il.com;
> weiyongjun (A) <weiyongjun1@...wei.com>; eric.dumazet@...il.com;
> Jason Wang <jasowang@...hat.com>
> Subject: [PATCH net V3 2/2] tuntap: synchronize through tfiles array instead
> of tun->numqueues
> 
> When a queue(tfile) is detached through __tun_detach(), we move the
> last enabled tfile to the position where detached one sit but don't
> NULL out last position. We expect to synchronize the datapath through
> tun->numqueues. Unfortunately, this won't work since we're lacking
> sufficient mechanism to order or synchronize the access to
> tun->numqueues.
> 
> To fix this, NULL out the last position during detaching and check
> RCU protected tfile against NULL instead of checking tun->numqueues in
> datapath.
> 
> Cc: YueHaibing <yuehaibing@...wei.com>
> Cc: Cong Wang <xiyou.wangcong@...il.com>
> Cc: weiyongjun (A) <weiyongjun1@...wei.com>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Fixes: c8d68e6be1c3b ("tuntap: multiqueue support")
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
> Changes from V2:
> - resample during detach in tun_xdp_xmit()
> Changes from V1:
> - keep the check in tun_xdp_xmit()
> ---

Reviewed-by: Wei Yongjun <weiyongjun1@...wei.com>

Thanks