netdev - Re: [PATCH net-next v3 15/16] net/mlx5e: take the rtnl lock when calling netif_set_xps

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <161597134352.3996.436408610278743110@kwain.local>
Date:   Wed, 17 Mar 2021 09:55:43 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     Maxim Mykytianskyi <maximmi@...dia.com>,
        Saeed Mahameed <saeed@...nel.org>,
        Tariq Toukan <tariqt@...dia.com>, alexander.duyck@...il.com,
        davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 15/16] net/mlx5e: take the rtnl lock when calling netif_set_xps_queue

Quoting Saeed Mahameed (2021-03-12 21:54:18)
> On Fri, 2021-03-12 at 16:04 +0100, Antoine Tenart wrote:
> > netif_set_xps_queue must be called with the rtnl lock taken, and this
> > is
> > now enforced using ASSERT_RTNL(). mlx5e_attach_netdev was taking the
> > lock conditionally, fix this by taking the rtnl lock all the time.
> 
> There is a reason why it is conditional:
> we had a bug in the past of double locking here:
> 
> [ 4255.283960] echo/644 is trying to acquire lock:
> 
>  [ 4255.285092] ffffffff85101f90 (rtnl_mutex){+..}, at:
> mlx5e_attach_netdev0xd4/0×3d0 [mlx5_core]
> 
>  [ 4255.287264] 
> 
>  [ 4255.287264] but task is already holding lock:
> 
>  [ 4255.288971] ffffffff85101f90 (rtnl_mutex){+..}, at:
> ipoib_vlan_add0×7c/0×2d0 [ib_ipoib]
> 
> ipoib_vlan_add is called under rtnl and will eventually call 
> mlx5e_attach_netdev, we don't have much control over this in mlx5
> driver since the rdma stack provides a per-prepared netdev to attach to
> our hw. maybe it is time we had a nested rtnl lock .. 

Not sure we want to add a nested rtnl lock because of xps. I'd like to
see other options first. Could be having a locking mechanism for xps not
relying on rtnl; if that's possible.

As for this series, patches 6, 15 (this one) and 16 are not linked to
and do not rely on the other patches. They're improvement or fixes for
already existing behaviours. The series already gained enough new
patches since v1 and I don't want to maintain it out-of-tree for too
long, so I'll resend it without patches 6, 15 and 16; and then we'll be
able to focus on the xps locking relationship with rtnl.

Antoine