From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci@vger.kernel.org, Hari Vyas <hari.vyas@broadcom.com>,
Ray Jui <ray.jui@broadcom.com>,
Srinath Mannam <srinath.mannam@broadcom.com>,
Guenter Roeck <linux@roeck-us.net>, Jens Axboe <axboe@kernel.dk>,
Lukas Wunner <lukas@wunner.de>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Marta Rybczynska <mrybczyn@kalray.eu>,
Pierre-Yves Kerbrat <pkerbrat@kalray.eu>,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 2/6] pci: Set pci_dev->is_added before calling device_add
Date: Sat, 18 Aug 2018 13:28:15 +1000 [thread overview]
Message-ID: <8dafc92f9c9cefba89ec1ec9839d086540af4557.camel@kernel.crashing.org> (raw)
In-Reply-To: <20180817162534.GD128050@bhelgaas-glaptop.roam.corp.google.com>
On Fri, 2018-08-17 at 11:25 -0500, Bjorn Helgaas wrote:
> On Fri, Aug 17, 2018 at 02:48:58PM +1000, Benjamin Herrenschmidt wrote:
> > This re-fixes the bug reported by Hari Vyas <hari.vyas@broadcom.com>
> > after my revert of his commit but in a much simpler way.
> >
> > The main issues is that is_added was being set after the driver
> > got bound and started, and thus setting it could race with other
> > changes to struct pci_dev.
>
> The "bind driver, then set dev->added = 1" order seems to have been
> there since the beginning of dev->is_added:
>
> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8a1bc9013a03
>
> This patch seems reasonable, but I'm a little dubious about the
> existence of "is_added" in the first place. As far as I can tell, the
> only other buses with something similar are the MEN Chameleon bus and
> the Intel Management Engine Interface.
>
> The PCI uses of "is_added" don't seem *that* critical or unique to
> PCI, so I'm not 100% convinced we need it at all. But I haven't
> looked into it enough to be able to propose an alternative.
This is a whole different conversation you are taking us into :-)
is_added is currently needed for a number of reasons, mostly relating
to partial hotplug, and historically comes from the fact that we
separated the PCI probing & tree construction from the registration
with the device-model. This of course comes from the fact that the
device model didn't actually exist yet when the PCI code was
created :-)
So let's keep things separate shall we ? I'd rather fix this correctly
now, and get rid of that pesky atomic priv_flags which I think is just
going to be a long term add to the mess rather than an improvement, and
separately we can discuss whether is_added is something that can go
away, but I suspect this will come in the form of either a deeper
rework of how we do PCI probing, or simply finding a struct device/kobj
field we can use as a hint that we've added the device already for
hotplug.
> > This fixes it by setting the flag first, which also has the
> > advantage of matching the fact that we are clearing it *after*
> > unbinding in the remove path, thus the flag is now symtetric
> > and always set while the driver code is running.
> >
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> > drivers/pci/bus.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> > index 35b7fc87eac5..48ae63673aa8 100644
> > --- a/drivers/pci/bus.c
> > +++ b/drivers/pci/bus.c
> > @@ -321,16 +321,16 @@ void pci_bus_add_device(struct pci_dev *dev)
> > pci_proc_attach_device(dev);
> > pci_bridge_d3_update(dev);
> >
> > + dev->is_added = 1;
> > dev->match_driver = true;
> > retval = device_attach(&dev->dev);
> > if (retval < 0 && retval != -EPROBE_DEFER) {
> > + dev->is_added = 0;
> > pci_warn(dev, "device attach failed (%d)\n", retval);
> > pci_proc_detach_device(dev);
> > pci_remove_sysfs_dev_files(dev);
> > return;
> > }
> > -
> > - dev->is_added = 1;
> > }
> > EXPORT_SYMBOL_GPL(pci_bus_add_device);
> >
> > --
> > 2.17.1
> >
next prev parent reply other threads:[~2018-08-18 3:28 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-17 4:48 [RFC PATCH 0/6] pci: Rework is_added race fix and address bridge enable races Benjamin Herrenschmidt
2018-08-17 4:48 ` [RFC PATCH 1/6] Revert "PCI: Fix is_added/is_busmaster race condition" Benjamin Herrenschmidt
2018-08-17 4:57 ` Benjamin Herrenschmidt
2018-08-17 15:44 ` Bjorn Helgaas
2018-08-18 3:24 ` Benjamin Herrenschmidt
2018-08-19 2:24 ` Bjorn Helgaas
2018-08-20 2:10 ` Benjamin Herrenschmidt
2018-08-20 6:25 ` Hari Vyas
2018-08-20 11:09 ` Benjamin Herrenschmidt
2018-08-20 11:43 ` Hari Vyas
2018-08-20 7:17 ` Lukas Wunner
2018-08-20 11:12 ` Benjamin Herrenschmidt
2018-08-17 4:48 ` [RFC PATCH 2/6] pci: Set pci_dev->is_added before calling device_add Benjamin Herrenschmidt
2018-08-17 4:57 ` Benjamin Herrenschmidt
2018-08-17 16:25 ` Bjorn Helgaas
2018-08-17 18:15 ` Lukas Wunner
2018-08-18 3:41 ` Benjamin Herrenschmidt
2018-08-18 3:28 ` Benjamin Herrenschmidt [this message]
2018-08-17 4:48 ` [RFC PATCH 3/6] pci: Remove priv_flags and use dev->error_state for "disconnected" status Benjamin Herrenschmidt
2018-08-17 5:13 ` [RFC PATCH v2 " Benjamin Herrenschmidt
2018-08-17 4:49 ` [RFC PATCH 4/6] pci: Add a mutex to pci_dev to protect device state Benjamin Herrenschmidt
2018-08-17 4:49 ` [RFC PATCH 5/6] pci: Protect the enable/disable state of pci_dev using the state mutex Benjamin Herrenschmidt
2018-08-17 8:09 ` Marta Rybczynska
2018-08-17 8:30 ` Benjamin Herrenschmidt
2018-08-17 9:00 ` Hari Vyas
2018-08-17 9:39 ` Benjamin Herrenschmidt
2018-08-17 10:10 ` Hari Vyas
2018-08-17 10:24 ` Benjamin Herrenschmidt
2018-08-17 4:49 ` [RFC PATCH 6/6] pci: Protect is_busmaster using the state lock Benjamin Herrenschmidt
2018-08-17 5:03 ` [RFC PATCH 0/6] pci: Rework is_added race fix and address bridge enable races Benjamin Herrenschmidt
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