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Fri, 05 Feb 2021 02:16:11 -0800 (PST) MIME-Version: 1.0 References: <20210204165831.2703772-2-daniel.vetter@ffwll.ch> <20210204215019.GA104698@bjorn-Precision-5520> <20210204222407.pkx7wvmcvugdwqdd@pali> <20210205100449.w2vzqozgnolxqh4h@pali> In-Reply-To: <20210205100449.w2vzqozgnolxqh4h@pali> From: Daniel Vetter Date: Fri, 5 Feb 2021 11:16:00 +0100 Message-ID: Subject: Re: [PATCH 1/2] PCI: also set up legacy files only after sysfs init To: =?UTF-8?Q?Pali_Roh=C3=A1r?= Cc: Bjorn Helgaas , LKML , Stephen Rothwell , linux-samsung-soc , Jan Kara , Kees Cook , Greg Kroah-Hartman , Linux PCI , Linux MM , Jason Gunthorpe , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , John Hubbard , Bjorn Helgaas , Daniel Vetter , Dan Williams , Andrew Morton , Linux ARM , "open list:DMA BUFFER SHARING FRAMEWORK" , "Oliver O'Halloran" , =?UTF-8?Q?Krzysztof_Wilczy=C5=84ski?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 750911042 X-Stat-Signature: 9bbzi1krdajmp387eekma8d6ieksi5f6 Received-SPF: none (ffwll.ch>: No applicable sender policy available) receiver=imf04; identity=mailfrom; envelope-from=""; helo=mail-oi1-f176.google.com; client-ip=209.85.167.176 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1612520171-140377 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Feb 5, 2021 at 11:04 AM Pali Roh=C3=A1r wrote: > > On Friday 05 February 2021 10:59:50 Daniel Vetter wrote: > > On Thu, Feb 4, 2021 at 11:24 PM Pali Roh=C3=A1r wrote= : > > > > > > On Thursday 04 February 2021 15:50:19 Bjorn Helgaas wrote: > > > > [+cc Oliver, Pali, Krzysztof] > > > > > > Just to note that extending or using sysfs_initialized introduces > > > another race condition into kernel code which results in PCI fatal > > > errors. Details are in email discussion which Bjorn already sent. > > > > Yeah I wondered why this doesn't race. > > It races, but with smaller probability. I have not seen this race > condition on x86. But I was able to reproduce it with native PCIe > drivers on ARM64 (Marvell Armada 3720; pci-aardvark). In mentioned > discussion I wrote when this race condition happen. But I understand > that it is hard to simulate it. btw I looked at your patch, and isn't that just reducing the race window? I think we have a very similar problem in drm, where the drm_dev_register() for the overall device (which also registers all drm_connector) can race with the hotplug of an individual connector in drm_connector_register() which is hotplugged at runtime. I went with a per-connector registered boolean + a lock to make sure that really only one of the two call paths can end up registering the connector. Part of registering connectors is setting up sysfs files, so I think it's exactly the same problem as here. Cheers, Daniel > > > but since the history goes back > > to pre-git times I figured it would have been addressed somehow > > already if it indeed does race. > > -Daniel > > > > > > s/also/Also/ in subject > > > > > > > > On Thu, Feb 04, 2021 at 05:58:30PM +0100, Daniel Vetter wrote: > > > > > We are already doing this for all the regular sysfs files on PCI > > > > > devices, but not yet on the legacy io files on the PCI buses. Thu= s far > > > > > now problem, but in the next patch I want to wire up iomem revoke > > > > > support. That needs the vfs up an running already to make so that > > > > > iomem_get_mapping() works. > > > > > > > > s/now problem/no problem/ > > > > s/an running/and running/ > > > > s/so that/sure that/ ? > > > > > > > > iomem_get_mapping() doesn't exist; I don't know what that should be= . > > > > > > > > > Wire it up exactly like the existing code. Note that > > > > > pci_remove_legacy_files() doesn't need a check since the one for > > > > > pci_bus->legacy_io is sufficient. > > > > > > > > I'm not sure exactly what you mean by "the existing code." I could > > > > probably figure it out, but it would save time to mention the exist= ing > > > > function here. > > > > > > > > This looks like another instance where we should really apply Olive= r's > > > > idea of converting these to attribute_groups [1]. > > > > > > > > The cover letter mentions options discussed with Greg in [2], but I > > > > don't think the "sysfs_initialized" hack vs attribute_groups was pa= rt > > > > of that discussion. > > > > > > > > It's not absolutely a show-stopper, but it *is* a shame to extend t= he > > > > sysfs_initialized hack if attribute_groups could do this more clean= ly > > > > and help solve more than one issue. > > > > > > > > Bjorn > > > > > > > > [1] https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704= ZEwLKGXQzBfqaA@mail.gmail.com > > > > [2] https://lore.kernel.org/dri-devel/CAKMK7uGrdDrbtj0OyzqQc0CGrQwc= 2F3tFJU9vLfm2jjufAZ5YQ@mail.gmail.com/ > > > > > > > > > Signed-off-by: Daniel Vetter > > > > > Cc: Stephen Rothwell > > > > > Cc: Jason Gunthorpe > > > > > Cc: Kees Cook > > > > > Cc: Dan Williams > > > > > Cc: Andrew Morton > > > > > Cc: John Hubbard > > > > > Cc: J=C3=A9r=C3=B4me Glisse > > > > > Cc: Jan Kara > > > > > Cc: Dan Williams > > > > > Cc: Greg Kroah-Hartman > > > > > Cc: linux-mm@kvack.org > > > > > Cc: linux-arm-kernel@lists.infradead.org > > > > > Cc: linux-samsung-soc@vger.kernel.org > > > > > Cc: linux-media@vger.kernel.org > > > > > Cc: Bjorn Helgaas > > > > > Cc: linux-pci@vger.kernel.org > > > > > --- > > > > > drivers/pci/pci-sysfs.c | 7 +++++++ > > > > > 1 file changed, 7 insertions(+) > > > > > > > > > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > > > > > index fb072f4b3176..0c45b4f7b214 100644 > > > > > --- a/drivers/pci/pci-sysfs.c > > > > > +++ b/drivers/pci/pci-sysfs.c > > > > > @@ -927,6 +927,9 @@ void pci_create_legacy_files(struct pci_bus *= b) > > > > > { > > > > > int error; > > > > > > > > > > + if (!sysfs_initialized) > > > > > + return; > > > > > + > > > > > b->legacy_io =3D kcalloc(2, sizeof(struct bin_attribute), > > > > > GFP_ATOMIC); > > > > > if (!b->legacy_io) > > > > > @@ -1448,6 +1451,7 @@ void pci_remove_sysfs_dev_files(struct pci_= dev *pdev) > > > > > static int __init pci_sysfs_init(void) > > > > > { > > > > > struct pci_dev *pdev =3D NULL; > > > > > + struct pci_bus *pbus =3D NULL; > > > > > int retval; > > > > > > > > > > sysfs_initialized =3D 1; > > > > > @@ -1459,6 +1463,9 @@ static int __init pci_sysfs_init(void) > > > > > } > > > > > } > > > > > > > > > > + while ((pbus =3D pci_find_next_bus(pbus))) > > > > > + pci_create_legacy_files(pbus); > > > > > + > > > > > return 0; > > > > > } > > > > > late_initcall(pci_sysfs_init); > > > > > -- > > > > > 2.30.0 > > > > > > > > > > > > > > > _______________________________________________ > > > > > linux-arm-kernel mailing list > > > > > linux-arm-kernel@lists.infradead.org > > > > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > > > > > > > -- > > Daniel Vetter > > Software Engineer, Intel Corporation > > http://blog.ffwll.ch --=20 Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch