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

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Message-Id: <20190509.092242.151546265607007899.davem@davemloft.net>
Date:   Thu, 09 May 2019 09:22:42 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jasowang@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        yuehaibing@...wei.com, xiyou.wangcong@...il.com,
        weiyongjun1@...wei.com, eric.dumazet@...il.com
Subject: Re: [PATCH net V3 2/2] tuntap: synchronize through tfiles array
 instead of tun->numqueues

From: Jason Wang <jasowang@...hat.com>
Date: Wed,  8 May 2019 23:20:18 -0400

> 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()

Applied and queued up for -stable.