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Date:   Thu, 4 Feb 2021 23:24:07 +0100
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        LKML <linux-kernel@vger.kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        linux-samsung-soc@vger.kernel.org, Jan Kara <jack@suse.cz>,
        Kees Cook <keescook@chromium.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-pci@vger.kernel.org, linux-mm@kvack.org,
        Jason Gunthorpe <jgg@ziepe.ca>,
        =?utf-8?B?SsOpcsO0bWU=?= Glisse <jglisse@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org,
        Oliver O'Halloran <oohall@gmail.com>,
        Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kw@linux.com>
Subject: Re: [PATCH 1/2] PCI: also set up legacy files only after sysfs init
Message-ID: <20210204222407.pkx7wvmcvugdwqdd@pali>
References: <20210204165831.2703772-2-daniel.vetter@ffwll.ch>
 <20210204215019.GA104698@bjorn-Precision-5520>
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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.

> 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. Thus 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 existing
> function here.
> 
> This looks like another instance where we should really apply Oliver'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 part
> of that discussion.
> 
> It's not absolutely a show-stopper, but it *is* a shame to extend the
> sysfs_initialized hack if attribute_groups could do this more cleanly
> and help solve more than one issue.
> 
> Bjorn
> 
> [1] https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704ZEwLKGXQzBfqaA@mail.gmail.com
> [2] https://lore.kernel.org/dri-devel/CAKMK7uGrdDrbtj0OyzqQc0CGrQwc2F3tFJU9vLfm2jjufAZ5YQ@mail.gmail.com/
> 
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Kees Cook <keescook@chromium.org>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Jérôme Glisse <jglisse@redhat.com>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > 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 <bhelgaas@google.com>
> > 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 = 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 = NULL;
> > +	struct pci_bus *pbus = NULL;
> >  	int retval;
> >  
> >  	sysfs_initialized = 1;
> > @@ -1459,6 +1463,9 @@ static int __init pci_sysfs_init(void)
> >  		}
> >  	}
> >  
> > +	while ((pbus = 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