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

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Date: Fri, 10 May 2024 21:22:31 +0200
From: Klara Modin <klarasmodin@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Lukas Wunner <lukas@...ner.de>
Cc: bcfradella@...ton.me, Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
 Danil Rybakov <danilrybakov249@...il.com>,
 Hans de Goede <hdegoede@...hat.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 platform-driver-x86@...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 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>