linux-kernel - Re: [PATCH net-next] netdevsim: Register and unregister devlink traps on probe/remove device

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Message-ID: <YXZB/3+IR6I0b2xE@unreal>
Date:   Mon, 25 Oct 2021 08:34:55 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Ido Schimmel <idosch@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org,
        syzbot+93d5accfaefceedf43c1@...kaller.appspotmail.com
Subject: Re: [PATCH net-next] netdevsim: Register and unregister devlink
 traps on probe/remove device

On Sun, Oct 24, 2021 at 01:48:25PM +0300, Ido Schimmel wrote:
> On Sun, Oct 24, 2021 at 12:54:52PM +0300, Leon Romanovsky wrote:
> > On Sun, Oct 24, 2021 at 12:05:12PM +0300, Ido Schimmel wrote:
> > > On Sun, Oct 24, 2021 at 11:42:11AM +0300, Leon Romanovsky wrote:
> > > > From: Leon Romanovsky <leonro@...dia.com>
> > > > 
> > > > Align netdevsim to be like all other physical devices that register and
> > > > unregister devlink traps during their probe and removal respectively.
> > > 
> > > No, this is incorrect. Out of the three drivers that support both reload
> > > and traps, both netdevsim and mlxsw unregister the traps during reload.
> > > Here is another report from syzkaller about mlxsw [1].
> > 
> > Sorry, I overlooked it.
> > 
> > > 
> > > Please revert both 22849b5ea595 ("devlink: Remove not-executed trap
> > > policer notifications") and 8bbeed485823 ("devlink: Remove not-executed
> > > trap group notifications").
> > 
> > However, before we rush and revert commit, can you please explain why
> > current behavior to reregister traps on reload is correct?
> > 
> > I think that you are not changing traps during reload, so traps before
> > reload will be the same as after reload, am I right?
> 
> During reload we tear down the entire driver and load it again. As part
> of the reload_down() operation we tear down the various objects from
> both devlink and the device (e.g., shared buffer, ports, traps, etc.).
> As part of the reload_up() operation we issue a device reset and
> register everything back.

This is an implementation which is arguably questionable and pinpoints
problem with devlink reload. It mixes different SW layers into one big
mess which I tried to untangle.

The devlink "feature" that driver reregisters itself again during execution
of other user-visible devlink command can't be right design.

> 
> While the list of objects doesn't change, their properties (e.g., shared
> buffer size, trap action, policer rate) do change back to the default
> after reload and we cannot go back on that as it's a user-visible
> change.

I don't propose to go back, just prefer to see fixed mlxsw that
shouldn't touch already created and registered objects from net/core/devlink.c.

All reset-to-default should be performed internally to the driver
without any need to devlink_*_register() again, so we will be able to
clean rest devlink notifications.

So at least for the netdevsim, this change looks like the correct one,
while mlxsw should be fixed next.

Thanks