linux-kernel - Re: [PATCH] PCI: vmd: guard device addition and removal

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Message-ID: <5930238.lOV4Wx5bFT@steina-w>
Date:   Tue, 11 Apr 2023 08:29:20 +0200
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     "You-Sheng Yang (vicamo)" <vicamo.yang@...onical.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Nirmal Patel <nirmal.patel@...ux.intel.com>,
        Jonathan Derrick <jonathan.derrick@...ux.dev>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Keith Busch <kbusch@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Korneliusz Osmenda <korneliuszo@...il.com>
Subject: Re: [PATCH] PCI: vmd: guard device addition and removal

Am Samstag, 8. April 2023, 01:58:29 CEST schrieb Bjorn Helgaas:
> [+cc Korneliusz, Alexander]
> 
> On Tue, Mar 14, 2023 at 01:37:33AM +0800, You-Sheng Yang (vicamo) wrote:
> > VMD may fail to create sysfs entries while `pci_rescan_bus()` called in
> > 
> > some other drivers like t7xx wwan driver:
> >   sysfs: cannot create duplicate filename '/devices/.../resource0'
> >   
> >   Call Trace:
> >    <TASK>
> >    sysfs_warn_dup.cold+0x17/0x34
> >    sysfs_add_bin_file_mode_ns+0xc0/0xf0
> >    sysfs_create_bin_file+0x6d/0xb0
> >    pci_create_attr+0x117/0x260
> >    pci_create_resource_files+0x6b/0x150
> >    pci_create_sysfs_dev_files+0x18/0x30
> >    pci_bus_add_device+0x30/0x80
> >    pci_bus_add_devices+0x31/0x80
> >    pci_bus_add_devices+0x5b/0x80
> >    vmd_enable_domain.constprop.0+0x6b7/0x880 [vmd]
> >    vmd_probe+0x16d/0x193 [vmd]
> 
> This is a long-standing issue, and I would *love* to nail it, but this
> doesn't feel like the right solution to me.  What's unique about vmd
> here?
> 
> I guess maybe it's similar to the situation Korneliusz and Alexander
> ran into at [1]?

What's the other path creating those sysfs files? Also vmd seems to be built 
as a module in this case. So that's a different issue. pci-imx6 is racing 
against an initcall when being built into the kernel. The probe_type 
PROBE_PREFER_ASYNCHRONOUS is also important.
Being built as a module this race is essentially impossible.

Best regards,
Alexander

> And why is t7xx called out specifically here?  This is a pretty
> generic sysfs attribute issue and it doesn't *seem* like t7xx should
> be special in that respect.  Oooh, maybe it's the fact that there's a
> t7xx patch [2] coming that adds pci_rescan_bus() there?
> 
> Krzysztof has converted a lot of the sysfs files to static attributes,
> e.g.,
> 
>   506140f9c06b ("PCI/sysfs: Convert "index", "acpi_index", "label" to static
> attributes") d93f8399053d ("PCI/sysfs: Convert "vpd" to static attribute")
>   f42c35ea3b13 ("PCI/sysfs: Convert "reset" to static attribute")
>   527139d738d7 ("PCI/sysfs: Convert "rom" to static attribute")
>   e1d3f3268b0e ("PCI/sysfs: Convert "config" to static attribute")
> 
> I think that's the *best* approach since the sysfs infrastructure
> already prevents races here.  But these last few files are more
> difficult to convert, so we've been kind of stalled on them.
> 
> Bjorn
> 
> [1]
> https://lore.kernel.org/r/20230316091540.494366-1-alexander.stein@ew.tq-gro
> up.com [2]
> https://lore.kernel.org/linux-pci/20230124204543.550d88e3@kernel.org/
> > Fixes: 185a383ada2e ("x86/PCI: Add driver for Intel Volume Management
> > Device (VMD)") Signed-off-by: You-Sheng Yang (vicamo)
> > <vicamo.yang@...onical.com> ---
> > 
> >  drivers/pci/controller/vmd.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> > index 769eedeb8802..f050991bd1e9 100644
> > --- a/drivers/pci/controller/vmd.c
> > +++ b/drivers/pci/controller/vmd.c
> > @@ -838,9 +838,13 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> > unsigned long features)> 
> >  	pci_add_resource_offset(&resources, &vmd->resources[1], offset[0]);
> >  	pci_add_resource_offset(&resources, &vmd->resources[2], offset[1]);
> > 
> > +	pci_lock_rescan_remove();
> > +
> > 
> >  	vmd->bus = pci_create_root_bus(&vmd->dev->dev, vmd->busn_start,
> >  	
> >  				       &vmd_ops, sd, &resources);
> >  	
> >  	if (!vmd->bus) {
> > 
> > +		pci_unlock_rescan_remove();
> > +
> > 
> >  		pci_free_resource_list(&resources);
> >  		vmd_remove_irq_domain(vmd);
> >  		return -ENODEV;
> > 
> > @@ -893,6 +897,8 @@ static int vmd_enable_domain(struct vmd_dev *vmd,
> > unsigned long features)> 
> >  	vmd_acpi_end();
> > 
> > +	pci_unlock_rescan_remove();
> > +
> > 
> >  	WARN(sysfs_create_link(&vmd->dev->dev.kobj, &vmd->bus->dev.kobj,
> >  	
> >  			       "domain"), "Can't create symlink to 
domain\n");
> >  	
> >  	return 0;


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