Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 10 Nov 2021 09:52:07 +0200
From:   Leon Romanovsky <leon@kernel.org>
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     Jason Gunthorpe <jgg@nvidia.com>, Jiri Pirko <jiri@nvidia.com>,
        Ido Schimmel <idosch@idosch.org>,
        Jiri Pirko <jiri@resnulli.us>,
        "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
Message-ID: <YYt6Jyyz+K9Pj3oL@unreal>
References: <YYlfI4UgpEsMt5QI@unreal>
 <20211108101646.0a4e5ca4@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
 <YYlrZZTdJKhha0FF@unreal>
 <20211108104608.378c106e@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
 <YYmBbJ5++iO4MOo7@unreal>
 <20211108153126.1f3a8fe8@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
 <20211109144358.GA1824154@nvidia.com>
 <20211109070702.17364ec7@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
 <20211109153335.GH1740502@nvidia.com>
 <20211109082042.31cf29c3@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20211109082042.31cf29c3@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Precedence: bulk

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.

It is important to add that this problem existed even before auxiliary
bus conversion.

Thanks