linux-kernel - Re: [PATCH] p2sb: Don't init until unassigned resources have been assigned.

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Message-ID: <am2n3qjaxgnciwfxhqs4aeosyug2oy2umuul4dzuagfhxdjlod@7ksrhwbjdxuc>
Date: Sun, 12 May 2024 10:23:02 +0000
From: Shinichiro Kawasaki <shinichiro.kawasaki@....com>
To: Klara Modin <klarasmodin@...il.com>
CC: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Lukas Wunner
	<lukas@...ner.de>, "bcfradella@...ton.me" <bcfradella@...ton.me>, Danil
 Rybakov <danilrybakov249@...il.com>, Hans de Goede <hdegoede@...hat.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	"platform-driver-x86@...r.kernel.org" <platform-driver-x86@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Ben Fradella
	<bfradell@...app.com>, Ranjan Dutta <ranjan.dutta@...el.com>, Yifan2 Li
	<yifan2.li@...el.com>, Jonathan Yong <jonathan.yong@...el.com>
Subject: Re: [PATCH] p2sb: Don't init until unassigned resources have been
 assigned.

On May 10, 2024 / 21:22, Klara Modin wrote:
> On 2024-05-10 16:50, Andy Shevchenko wrote:
> > On Thu, May 09, 2024 at 07:04:32PM +0200, Lukas Wunner wrote:
> > > [cc += Shin'ichiro, Klara, Andy, Danil]
> > 
> > Thank you!
> > 
> > > On Thu, May 09, 2024 at 04:49:34PM +0000, bcfradella@...ton.me wrote:
> > > > From: Ben Fradella <bfradell@...app.com>
> > > > 
> > > > The P2SB could get an invalid BAR from the BIOS, and that won't be fixed
> > > > up until pcibios_assign_resources(), which is an fs_initcall().
> > > > 
> > > > - Move p2sb_fs_init() to an fs_initcall_sync(). This is still early
> > > >    enough to avoid a race with any dependent drivers.
> > > > 
> > > > - Add a check for IORESOURCE_UNSET in p2sb_valid_resource() to catch
> > > >    unset BARs going forward.
> > > > 
> > > > - Return error values from p2sb_fs_init() so that the 'initcall_debug'
> > > >    cmdline arg provides useful data.
> > 
> > ...
> > 
> > > >   /*
> > > > - * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can
> > > > - * not be locked in sysfs pci bus rescan path because of deadlock. To
> > > > - * avoid the deadlock, access to P2SB devices with the lock at an early
> > > > - * step in kernel initialization and cache required resources. This
> > > > - * should happen after subsys_initcall which initializes PCI subsystem
> > > > - * and before device_initcall which requires P2SB resources.
> > > > + * pci_rescan_remove_lock() can not be locked in sysfs pci bus rescan path
> > 
> > PCI bus
> > 
> > > > + * because of deadlock. To avoid the deadlock, access P2SB devices with the lock
> > > > + * at an early step in kernel initialization and cache required resources.
> > > > + *
> > > > + * We want to run as early as possible. If the P2SB was assigned a bad BAR,
> > > > + * we'll need to wait on pcibios_assign_resources() to fix it. So, our list of
> > > > + * initcall dependencies looks something like this:
> > > > + *
> > > > + * ...
> > > > + * subsys_initcall (pci_subsys_init)
> > > > + * fs_initcall     (pcibios_assign_resources)
> > > >    */
> > 
> > This makes sense to me
> > Acked-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > 
> > I assume others will conduct the proper review and testing.
> > 
> 
> This patch did not introduce any new issues on my previously problematic
> system.
> 
> Tested-by: Klara Modin <klarasmodin@...il.com>

The changes look reasonable and good to me. I also confirmed that the patch
does not affect on my use case using two my test machines.

Reviewed-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>