radeon.ko/i586: BUG: kernel NULL pointer dereference, address:00000004

[kkabe at vega.pgw.jp]

Thanks you all for getting attention to the report: 

regressions at leemhuis.info sed in <55a3bbb1-5b3c-f454-b529-8ee9944cc67c at leemhuis.info>

>> On 14.07.23 05:12, Steven Rostedt wrote:
>> > On Fri, 14 Jul 2023 09:50:17 +0700
>> > Bagas Sanjaya <bagasdotme at gmail.com> wrote:
>> > 
>> >> I notice a regression report on Bugzilla [1]. Quoting from it:
>> >>
>> >>
>> >> See Bugzilla for the full thread and attached patches that fixes
>> >> this regression.
>> >>
>> >> Later, when bisecting, the reporter got better kernel trace:
>> >>
>> >>> [  469.825305] BUG: kernel NULL pointer dereference, address: 00000004
>> >>> [  469.830502] #PF: supervisor read access in kernel mode
>> >>> [  469.830502] #PF: error_code(0x0000) - not-present page
>> >>> [  469.830502] *pde = 00000000
>> >>> [  469.830502] Oops: 0000 [#1] PREEMPT SMP
>> >>> [  469.830502] CPU: 0 PID: 365 Comm: systemd-udevd Not tainted 5.14.0-221.el9.v1.i586 #1
>> > 
>> > This is a 5.14 kernel right?
>> 
>> And a vendor kernel that from the sound of the version number might be
>> heavily patched. But apparently the reporter later bisected this on a
>> newer kernel (Bagas, would have been good if this had been mentioned in
>> your earlier mail):
>> 
>> https://bugzilla.kernel.org/show_bug.cgi?id=217669#c5
>> ```
>> I succeeded to bisect down the regressing commit found in kernel-5.18.0-rc2:
>> 
>> b39181f7c690 (refs/bisect/bad) ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to
>> avoid adding weak function
>> 
>> This at a glance does not relate to drm/kms code.
>> 
>> The attached patch effectively reverts the commit for 32bit.
>> This fixed the problem on kernel-5.18.0, but not enough for kernel-6.4.3 ```
>> 
>> That being said: That commit is not in 5.18, as Steve noticed:
>> 
>> >> #regzbot introduced: b39181f7c6907d https://bugzilla.kernel.org/show_bug.cgi?id=217669
>> >> #regzbot title: FTRACE_MCOUNT_MAX_OFFSET causes kernel NULL pointer dereference and virtual console (tty1) freeze
>> > That commit was added in 5.19.
>> > 
>> > So I'm confused about why it's mentioned. Was it backported?
>> 
>> Taketo Kabe, could you please help to clean this confusion up? Did you
>> mean 5.19 in https://bugzilla.kernel.org/show_bug.cgi?id=217669#c5 ? And
>> BTW: did you really use a vanilla kernel for your bisection?


Reporter Me:
I bisected using freedesktop.org kernel tree, which git commit ID is
in sync with kernel.org
but version number in ./Makefile could be slighty behind. 

Patch in
https://bugzilla.kernel.org/show_bug.cgi?id=217669#c4
fixed the problem in freedesktop.org kernel 5.18.0-rc2 .
This may explain that in kernel.org tree, the said commit is in kernel-5.19.


>> TWIMC, there is also
>> https://bugzilla.kernel.org/show_bug.cgi?id=217669#c6 :
>> ```
>> Attached patch sort of fixes the problem; it does not panic and
>> KMS console works, but printk is triggered 4 times on radeon.ko load and
>> when VGA connector is plugged in.
>> 
>> I am sort of at loss now; I need advice from people which knows better.
>> 
>>  --- ./drivers/gpu/drm/drm_internal.h.rd	2023-06-25 21:35:27.506967450 +0900
>>  +++ ./drivers/gpu/drm/drm_internal.h.rd	2023-06-25 21:36:34.758055363 +0900
>>  @@ -99,6 +99,10 @@ u64 drm_vblank_count(struct drm_device *
>>   /* drm_vblank_work.c */
>>   static inline void drm_vblank_flush_worker(struct drm_vblank_crtc *vblank)
>>   {
>>  +	if (!vblank->worker) {
>>  +		printk(KERN_WARNING "%s: vblank->worker NULL? returning\n", __func__);
>>  +		return;
>>  +	}
>>   	kthread_flush_worker(vblank->worker);
>>   }
>> ```
>> 
>> Ciao, Thorsten
>>