Re: [PATCH net-next] devlink: Require devlink lock during device reload

From: Leon Romanovsky <leon@kernel.org>
To: Jiri Pirko <jiri@resnulli.us>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	Jakub Kicinski <kuba@kernel.org>, Jiri Pirko <jiri@nvidia.com>,
	Ido Schimmel <idosch@idosch.org>,
	"David S . Miller" <davem@davemloft.net>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	edwin.peer@broadcom.com
Subject: Re: [PATCH net-next] devlink: Require devlink lock during device reload
Date: Sun, 14 Nov 2021 08:19:02 +0200	[thread overview]
Message-ID: <YZCqVig9GQi/o1iz@unreal> (raw)
In-Reply-To: <YY4aEFkVuqR+vauw@nanopsycho>

On Fri, Nov 12, 2021 at 08:38:56AM +0100, Jiri Pirko wrote:
> Thu, Nov 11, 2021 at 01:17:52PM CET, leon@kernel.org wrote:
> >On Thu, Nov 11, 2021 at 01:05:11PM +0100, Jiri Pirko wrote:
> >> Tue, Nov 09, 2021 at 07:24:27PM CET, jgg@nvidia.com wrote:
> >> >On Tue, Nov 09, 2021 at 08:20:42AM -0800, Jakub Kicinski wrote:
> >> >> On Tue, 9 Nov 2021 11:33:35 -0400 Jason Gunthorpe wrote:
> >> >> > > > I once sketched out fixing this by removing the need to hold the
> >> >> > > > per_net_rwsem just for list iteration, which in turn avoids holding it
> >> >> > > > over the devlink reload paths. It seemed like a reasonable step toward
> >> >> > > > finer grained locking.  
> >> >> > > 
> >> >> > > Seems to me the locking is just a symptom.  
> >> >> > 
> >> >> > My fear is this reload during net ns destruction is devlink uAPI now
> >> >> > and, yes it may be only a symptom, but the root cause may be unfixable
> >> >> > uAPI constraints.
> >> >> 
> >> >> If I'm reading this right it locks up 100% of the time, what is a uAPI
> >> >> for? DoS? ;)
> >> >> 
> >> >> Hence my questions about the actual use cases.
> >> >
> >> >Removing namespace support from devlink would solve the crasher. I
> >> >certainly didn't feel bold enough to suggest such a thing :)
> >> >
> >> >If no other devlink driver cares about this it is probably the best
> >> >idea.
> >> 
> >> Devlink namespace support is not generic, not related to any driver.
> >
> >What do you mean?
> >
> >devlink_pernet_pre_exit() calls to devlink reload, which means that only
> >drivers that support reload care about it. The reload is driver thing.
> 
> However, Jason was talking about "namespace support removal from
> devlink"..

The code that sparkles deadlocks is in devlink_pernet_pre_exit() and
this will be nice to remove. I just don't know if it is possible to do
without ripping whole namespace support from devlink.

Thanks

> 
> 
> >
> >Thanks
> >
> >> 
> >> >
> >> >Jason