From: Cornelia Huck <cohuck@redhat.com>
To: Parav Pandit <parav@mellanox.com>
Cc: "alex.williamson@redhat.com" <alex.williamson@redhat.com>,
Jiri Pirko <jiri@mellanox.com>,
"kwankhede@nvidia.com" <kwankhede@nvidia.com>,
"davem@davemloft.net" <davem@davemloft.net>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH v2 1/6] mdev: Introduce sha1 based mdev alias
Date: Fri, 30 Aug 2019 16:02:23 +0200 [thread overview]
Message-ID: <20190830160223.332fd81f.cohuck@redhat.com> (raw)
In-Reply-To: <AM0PR05MB486621283F935B673455DA63D1BD0@AM0PR05MB4866.eurprd05.prod.outlook.com>
On Fri, 30 Aug 2019 12:58:04 +0000
Parav Pandit <parav@mellanox.com> wrote:
> > -----Original Message-----
> > From: Cornelia Huck <cohuck@redhat.com>
> > Sent: Friday, August 30, 2019 6:09 PM
> > To: Parav Pandit <parav@mellanox.com>
> > Cc: alex.williamson@redhat.com; Jiri Pirko <jiri@mellanox.com>;
> > kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org; linux-
> > kernel@vger.kernel.org; netdev@vger.kernel.org
> > Subject: Re: [PATCH v2 1/6] mdev: Introduce sha1 based mdev alias
> >
> > On Fri, 30 Aug 2019 12:33:22 +0000
> > Parav Pandit <parav@mellanox.com> wrote:
> >
> > > > -----Original Message-----
> > > > From: Cornelia Huck <cohuck@redhat.com>
> > > > Sent: Friday, August 30, 2019 2:47 PM
> > > > To: Parav Pandit <parav@mellanox.com>
> > > > Cc: alex.williamson@redhat.com; Jiri Pirko <jiri@mellanox.com>;
> > > > kwankhede@nvidia.com; davem@davemloft.net; kvm@vger.kernel.org;
> > > > linux- kernel@vger.kernel.org; netdev@vger.kernel.org
> > > > Subject: Re: [PATCH v2 1/6] mdev: Introduce sha1 based mdev alias
> > > >
> > > > On Thu, 29 Aug 2019 06:18:59 -0500
> > > > Parav Pandit <parav@mellanox.com> wrote:
> > > >
> > > > > Some vendor drivers want an identifier for an mdev device that is
> > > > > shorter than the UUID, due to length restrictions in the consumers
> > > > > of that identifier.
> > > > >
> > > > > Add a callback that allows a vendor driver to request an alias of
> > > > > a specified length to be generated for an mdev device. If
> > > > > generated, that alias is checked for collisions.
> > > > >
> > > > > It is an optional attribute.
> > > > > mdev alias is generated using sha1 from the mdev name.
> > > > >
> > > > > Signed-off-by: Parav Pandit <parav@mellanox.com>
> > > > >
> > > > > ---
> > > > > Changelog:
> > > > > v1->v2:
> > > > > - Kept mdev_device naturally aligned
> > > > > - Added error checking for crypt_*() calls
> > > > > - Corrected a typo from 'and' to 'an'
> > > > > - Changed return type of generate_alias() from int to char*
> > > > > v0->v1:
> > > > > - Moved alias length check outside of the parent lock
> > > > > - Moved alias and digest allocation from kvzalloc to kzalloc
> > > > > - &alias[0] changed to alias
> > > > > - alias_length check is nested under get_alias_length callback
> > > > > check
> > > > > - Changed comments to start with an empty line
> > > > > - Fixed cleaunup of hash if mdev_bus_register() fails
> > > > > - Added comment where alias memory ownership is handed over to
> > > > > mdev device
> > > > > - Updated commit log to indicate motivation for this feature
> > > > > ---
> > > > > drivers/vfio/mdev/mdev_core.c | 123
> > > > ++++++++++++++++++++++++++++++-
> > > > > drivers/vfio/mdev/mdev_private.h | 5 +-
> > > > > drivers/vfio/mdev/mdev_sysfs.c | 13 ++--
> > > > > include/linux/mdev.h | 4 +
> > > > > 4 files changed, 135 insertions(+), 10 deletions(-)
> >
> > > > ...and detached from the local variable here. Who is freeing it? The
> > > > comment states that it is done by the mdev, but I don't see it?
> > > >
> > > mdev_device_free() frees it.
> >
> > Ah yes, I overlooked the kfree().
> >
> > > once its assigned to mdev, mdev is the owner of it.
> > >
> > > > This detour via the local variable looks weird to me. Can you either
> > > > create the alias directly in the mdev (would need to happen later in
> > > > the function, but I'm not sure why you generate the alias before
> > > > checking for duplicates anyway), or do an explicit copy?
> > > Alias duplicate check is done after generating it, because duplicate alias are
> > not allowed.
> > > The probability of collision is rare.
> > > So it is speculatively generated without hold the lock, because there is no
> > need to hold the lock.
> > > It is compared along with guid while mutex lock is held in single loop.
> > > And if it is duplicate, there is no need to allocate mdev.
> > >
> > > It will be sub optimal to run through the mdev list 2nd time after mdev
> > creation and after generating alias for duplicate check.
> >
> > Ok, but what about copying it? I find this "set local variable to NULL after
> > ownership is transferred" pattern a bit unintuitive. Copying it to the mdev (and
> > then unconditionally freeing it) looks more obvious to me.
> Its not unconditionally freed.
That's not what I have been saying :(
> Its freed in the error unwinding path.
> I think its ok along with the comment that describes this error path area.
It is not wrong, but I'm not sure I like it.
next prev parent reply other threads:[~2019-08-30 14:02 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 20:41 [PATCH 0/4] Introduce variable length mdev alias Parav Pandit
2019-08-26 20:41 ` [PATCH 1/4] mdev: Introduce sha1 based " Parav Pandit
2019-08-27 1:44 ` Alex Williamson
2019-08-27 1:51 ` Alex Williamson
2019-08-27 4:24 ` Parav Pandit
2019-08-27 10:24 ` Cornelia Huck
2019-08-27 11:12 ` Parav Pandit
2019-08-27 11:24 ` Cornelia Huck
2019-08-27 11:33 ` Parav Pandit
2019-08-27 11:41 ` Cornelia Huck
2019-08-27 11:57 ` Parav Pandit
2019-08-27 13:35 ` Cornelia Huck
2019-08-27 16:50 ` Alex Williamson
2019-08-27 11:16 ` Parav Pandit
2019-08-26 20:41 ` [PATCH 2/4] mdev: Make mdev alias unique among all mdevs Parav Pandit
2019-08-26 23:02 ` Mark Bloch
2019-08-27 4:28 ` Parav Pandit
2019-08-27 15:23 ` Alex Williamson
2019-08-27 16:16 ` Parav Pandit
2019-08-27 10:29 ` Cornelia Huck
2019-08-27 11:08 ` Parav Pandit
2019-08-27 11:29 ` Cornelia Huck
2019-08-27 15:28 ` Alex Williamson
2019-08-27 15:39 ` Cornelia Huck
2019-08-27 16:13 ` Parav Pandit
2019-08-27 16:24 ` Alex Williamson
2019-08-27 18:54 ` Parav Pandit
2019-08-26 20:41 ` [PATCH 3/4] mdev: Expose mdev alias in sysfs tree Parav Pandit
2019-08-27 1:53 ` Alex Williamson
2019-08-27 3:30 ` Parav Pandit
2019-08-27 10:47 ` Cornelia Huck
2019-08-27 11:07 ` Parav Pandit
2019-08-27 11:34 ` Cornelia Huck
2019-08-27 11:52 ` Parav Pandit
2019-08-27 11:55 ` Cornelia Huck
2019-08-27 12:00 ` Parav Pandit
2019-08-26 20:41 ` [PATCH 4/4] mtty: Optionally support mtty alias Parav Pandit
2019-08-27 13:11 ` [PATCH 0/4] Introduce variable length mdev alias Parav Pandit
2019-08-27 13:31 ` Cornelia Huck
2019-08-27 17:48 ` Alex Williamson
2019-08-27 18:11 ` Parav Pandit
2019-08-27 19:16 ` [PATCH v1 0/5] " Parav Pandit
2019-08-27 19:16 ` [PATCH v1 1/5] mdev: Introduce sha1 based " Parav Pandit
2019-08-28 21:25 ` Alex Williamson
2019-08-28 21:34 ` Alex Williamson
2019-08-29 9:07 ` Parav Pandit
2019-08-29 9:06 ` Parav Pandit
2019-08-27 19:16 ` [PATCH v1 2/5] mdev: Make mdev alias unique among all mdevs Parav Pandit
2019-08-28 21:36 ` Alex Williamson
2019-08-29 9:07 ` Parav Pandit
2019-08-27 19:16 ` [PATCH v1 3/5] mdev: Expose mdev alias in sysfs tree Parav Pandit
2019-08-27 19:16 ` [PATCH v1 4/5] mdev: Update sysfs documentation Parav Pandit
2019-08-27 19:16 ` [PATCH v1 5/5] mtty: Optionally support mtty alias Parav Pandit
2019-08-29 11:18 ` [PATCH v2 0/6] Introduce variable length mdev alias Parav Pandit
2019-08-29 11:18 ` [PATCH v2 1/6] mdev: Introduce sha1 based " Parav Pandit
2019-08-29 12:26 ` Yunsheng Lin
2019-08-30 2:27 ` Parav Pandit
2019-08-30 9:17 ` Cornelia Huck
2019-08-30 12:33 ` Parav Pandit
2019-08-30 12:39 ` Cornelia Huck
2019-08-30 12:58 ` Parav Pandit
2019-08-30 14:02 ` Cornelia Huck [this message]
2019-08-30 15:45 ` Parav Pandit
2019-09-02 14:46 ` Cornelia Huck
2019-09-03 3:47 ` Parav Pandit
2019-08-29 11:19 ` [PATCH v2 2/6] mdev: Make mdev alias unique among all mdevs Parav Pandit
2019-08-29 12:31 ` Yunsheng Lin
2019-08-30 12:40 ` Cornelia Huck
2019-08-30 12:59 ` Parav Pandit
2019-08-29 11:19 ` [PATCH v2 3/6] mdev: Expose mdev alias in sysfs tree Parav Pandit
2019-08-29 11:19 ` [PATCH v2 4/6] mdev: Introduce an API mdev_alias Parav Pandit
2019-08-29 11:19 ` [PATCH v2 5/6] mdev: Update sysfs documentation Parav Pandit
2019-08-30 12:49 ` Cornelia Huck
2019-08-30 13:10 ` Parav Pandit
2019-09-02 14:36 ` Cornelia Huck
2019-09-03 3:53 ` Parav Pandit
2019-08-29 11:19 ` [PATCH v2 6/6] mtty: Optionally support mtty alias Parav Pandit
2019-09-02 4:24 ` [PATCH v3 0/5] Introduce variable length mdev alias Parav Pandit
2019-09-02 4:24 ` [PATCH v3 1/5] mdev: Introduce sha1 based " Parav Pandit
2019-09-17 10:03 ` Cornelia Huck
2019-09-02 4:24 ` [PATCH v3 2/5] mdev: Make mdev alias unique among all mdevs Parav Pandit
2019-09-17 10:04 ` Cornelia Huck
2019-09-02 4:24 ` [PATCH v3 3/5] mdev: Expose mdev alias in sysfs tree Parav Pandit
2019-09-17 10:08 ` Cornelia Huck
2019-09-02 4:24 ` [PATCH v3 4/5] mdev: Introduce an API mdev_alias Parav Pandit
2019-09-17 10:10 ` Cornelia Huck
2019-09-02 4:24 ` [PATCH v3 5/5] mtty: Optionally support mtty alias Parav Pandit
2019-09-09 20:42 ` [PATCH v3 0/5] Introduce variable length mdev alias Parav Pandit
2019-09-11 13:56 ` Alex Williamson
2019-09-11 15:30 ` Parav Pandit
2019-09-11 16:29 ` Cornelia Huck
2019-09-11 16:38 ` Parav Pandit
2019-09-13 21:32 ` Alex Williamson
2019-09-13 23:19 ` Parav Pandit
2019-09-17 10:13 ` Cornelia Huck
2019-09-18 17:15 ` Parav Pandit
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