From: Jakub Kicinski <kuba@kernel.org>
To: Leon Romanovsky <leon@kernel.org>
Cc: "David S . Miller" <davem@davemloft.net>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
Andrew Lunn <andrew@lunn.ch>, Aya Levin <ayal@mellanox.com>,
Claudiu Manoil <claudiu.manoil@nxp.com>,
drivers@pensando.io, Florian Fainelli <f.fainelli@gmail.com>,
Ido Schimmel <idosch@nvidia.com>,
intel-wired-lan@lists.osuosl.org,
Ioana Ciornei <ioana.ciornei@nxp.com>,
Jesse Brandeburg <jesse.brandeburg@intel.com>,
Jiri Pirko <jiri@nvidia.com>,
linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org,
Michael Chan <michael.chan@broadcom.com>,
netdev@vger.kernel.org, oss-drivers@corigine.com,
Saeed Mahameed <saeedm@nvidia.com>,
Shannon Nelson <snelson@pensando.io>,
Simon Horman <simon.horman@corigine.com>,
Taras Chornyi <tchornyi@marvell.com>,
Tariq Toukan <tariqt@nvidia.com>,
Tony Nguyen <anthony.l.nguyen@intel.com>,
UNGLinuxDriver@microchip.com,
Vivien Didelot <vivien.didelot@gmail.com>,
Vladimir Oltean <vladimir.oltean@nxp.com>
Subject: Re: [PATCH net-next 5/6] devlink: Reshuffle resource registration logic
Date: Mon, 22 Nov 2021 18:27:28 -0800 [thread overview]
Message-ID: <20211122182728.370889f2@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <YZoHGKqLz6UBk2Sx@unreal>
On Sun, 21 Nov 2021 10:45:12 +0200 Leon Romanovsky wrote:
> On Fri, Nov 19, 2021 at 08:10:17AM -0800, Jakub Kicinski wrote:
> > On Fri, 19 Nov 2021 17:38:53 +0200 Leon Romanovsky wrote:
> > > My approach works, exactly like it works in other subsystems.
> > > https://lore.kernel.org/netdev/cover.1636390483.git.leonro@nvidia.com/
> >
> > What "other subsystems"? I'm aware of the RFC version of these patches.
>
> Approach to have fine-grained locking scheme, instead of having one big lock.
> This was done in MM for mmap_sem, we did it for RDMA too.
You're breaking things up to avoid lock ordering issues. The user can
still only run a single write command at a time.
> > Breaking up the locks to to protect sub-objects only is fine for
> > protecting internal lists but now you can't guarantee that the object
> > exists when driver is called.
>
> I can only guess about which objects you are talking.
It obviously refers to the port splitting I mentioned below.
> If you are talking about various devlink sub-objects (ports, traps,
> e.t.c), they created by the drivers and as such should be managed by them.
> Also they are connected to devlink which is guaranteed to exist. At the end,
> they called to devlink_XXX->devlink pointer without any existence check.
>
> If you are talking about devlink instance itself, we guarantee that it
> exists between devlink_alloc() and devlink_free(). It seems to me pretty
> reasonable request from drivers do not access devlink before devlink_alloc()
> or after devlink_free(),
>
> > I'm sure you'll utter your unprovable "in real drivers.." but the fact
> > is my approach does not suffer from any such issues. Or depends on
> > drivers registering devlink last.
>
> Registration of devlink doesn't do anything except opening it to the world.
> The lifetime is controlled with alloc and free. My beloved sentence "in
> real drivers ..." belongs to use of devlink_put and devlink_locks outside
> of devlink.c and nothing more.
As soon as there is a inter-dependency between two subsystems "must
be last" breaks down.
> > I can start passing a pointer to a devlink_port to split/unsplit
> > functions, which is a great improvement to the devlink driver API.
>
> You can do it with my approach too. We incremented reference counter
> of devlink instance when devlink_nl_cmd_port_split_doit() was called,
> and we can safely take devlink->port_list_lock lock before returning
> from pre_doit.
Wait, I thought you'd hold devlink->lock around split/unsplit.
Please look at the port splitting case, mlx5 doesn't implement it
but it's an important feature.
Either way, IDK how ref count on devlink helps with lifetime of a
subobject. You must assume the sub-objects can only be created outside
of the time devlink instance is visible or under devlink->lock?
next prev parent reply other threads:[~2021-11-23 2:27 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-17 18:26 [PATCH net-next 0/6] Devlink cleanups Leon Romanovsky
2021-11-17 18:26 ` [PATCH net-next 1/6] devlink: Remove misleading internal_flags from health reporter dump Leon Romanovsky
2021-11-17 18:26 ` [PATCH net-next 2/6] devlink: Delete useless checks of holding devlink lock Leon Romanovsky
2021-11-17 18:26 ` [PATCH net-next 3/6] devlink: Simplify devlink resources unregister call Leon Romanovsky
2021-11-17 18:26 ` [PATCH net-next 4/6] devlink: Clean registration of devlink port Leon Romanovsky
2021-11-18 4:49 ` Jakub Kicinski
2021-11-18 7:32 ` Leon Romanovsky
2021-11-17 18:26 ` [PATCH net-next 5/6] devlink: Reshuffle resource registration logic Leon Romanovsky
2021-11-18 4:49 ` Jakub Kicinski
2021-11-18 7:50 ` Leon Romanovsky
2021-11-19 1:48 ` Jakub Kicinski
2021-11-19 15:38 ` Leon Romanovsky
2021-11-19 16:10 ` Jakub Kicinski
2021-11-21 8:45 ` Leon Romanovsky
2021-11-23 2:27 ` Jakub Kicinski [this message]
2021-11-23 8:33 ` Leon Romanovsky
2021-11-23 23:33 ` Jakub Kicinski
2021-11-25 9:02 ` Leon Romanovsky
2021-11-17 18:26 ` [PATCH net-next 6/6] devlink: Inline sb related functions Leon Romanovsky
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