linux-kernel - Re: [PATCH v3 2/4] kernel: refactor lookup_or_create_module

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Message-ID: <4039ec74-8b46-417e-ad71-eff22239b90f@suse.com>
Date: Thu, 13 Feb 2025 16:55:54 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Shyam Saini <shyamsaini@...ux.microsoft.com>
Cc: linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org,
 code@...icks.com, linux@...musvillemoes.dk, christophe.leroy@...roup.eu,
 hch@...radead.org, mcgrof@...nel.org, frkaya@...ux.microsoft.com,
 vijayb@...ux.microsoft.com, petr.pavlu@...e.com, linux@...ssschuh.net,
 samitolvanen@...gle.com, da.gomez@...sung.com, gregkh@...uxfoundation.org,
 rafael@...nel.org, dakr@...nel.org
Subject: Re: [PATCH v3 2/4] kernel: refactor lookup_or_create_module_kobject()

On 2/11/25 22:48, Shyam Saini wrote:
> In the unlikely event of the allocation failing, it is better to let
> the machine boot with a not fully populated sysfs than to kill it with
> this BUG_ON(). All callers are already prepared for
> lookup_or_create_module_kobject() returning NULL.
> 
> This is also preparation for calling this function from non __init
> code, where using BUG_ON for allocation failure handling is not
> acceptable.

I think some error reporting should be cleaned up here.

The current situation is that locate_module_kobject() can fail in
several cases and all these situations are loudly reported by the
function, either by BUG_ON() or pr_crit(). Consistently with that, both
its current callers version_sysfs_builtin() and kernel_add_sysfs_param()
don't do any reporting if locate_module_kobject() fails; they simply
return.

The series seems to introduce two somewhat suboptimal cases.

With this patch, when either version_sysfs_builtin() or
kernel_add_sysfs_param() calls lookup_or_create_module_kobject() and it
fails because of a potential kzalloc() error, the problem is silently
ignored.

Similarly, in the patch #4, when module_add_driver() calls
lookup_or_create_module_kobject() and the function fails, the problem
may or may not be reported, depending on the error.

I'd suggest something as follows:
* Drop the pr_crit() reporting in lookup_or_create_module_kobject().
* Have version_sysfs_builtin() and kernel_add_sysfs_param() log an error
  when lookup_or_create_module_kobject() fails. Using BUG_ON() might be
  appropriate, as that is already what is used in
  kernel_add_sysfs_param()?
* Update module_add_driver() to propagate any error from
  lookup_or_create_module_kobject() up the stack.

-- 
Thanks,
Petr