Re: [PATCH v5] debugobjects: Don't call fill_pool() in early boot hardirq context

[Waiman Long <longman@redhat.com>]

On 6/7/26 1:15 AM, Ingo Molnar wrote:
> * Waiman Long <longman@redhat.com> wrote:
>
>> When booting a debug PREEMPT_RT kernel on an arm64 system with grace
>> processor, a "inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage"
>> lockdep warning message was reported to the console.
>>
>> During early boot, interrupts are getting enabled before the scheduler
>> is enabled. In this window (before SYSTEM_SCHEDULING is set) interrupts
>> can fire and attempt to fill the pool from within the hardirq. This can
>> lead to a deadlock the interrupt occurred while in the memory allocator.
>>
>> Add a new can_fill_pool() helper and reorder the exception rule and
>> forbid this scenario by excluding allocations from hardirq.
>>
>> Fixes: 06e0ae988f6e ("debugobjects: Allow to refill the pool before SYSTEM_SCHEDULING")
>> Co-developed-by: Waiman Long <longman@redhat.com>
>> Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
>> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Signed-off-by: Waiman Long <longman@redhat.com>
>> ---
>>   lib/debugobjects.c | 46 +++++++++++++++++++++++++++++++++++++---------
>>   1 file changed, 37 insertions(+), 9 deletions(-)
>>
>> diff --git a/lib/debugobjects.c b/lib/debugobjects.c
>> index b18a682fe3da..6fb00e08a4e2 100644
>> --- a/lib/debugobjects.c
>> +++ b/lib/debugobjects.c
>> @@ -720,6 +720,41 @@ static inline bool debug_objects_is_pi_blocked_on(void)
>>   #endif
>>   }
>>   
>> +static inline bool can_fill_pool(void)
>> +{
>> +	/*
>> +	 * On !RT enabled kernels there are no restrictions and spinlock_t and
>> +	 * raw_spinlock_t are the same types.
>> +	 */
>> +	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
>> +		return true;
>> -	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || system_state < SYSTEM_SCHEDULING ||
>> -	    (preemptible() && !debug_objects_is_pi_blocked_on())) {
>> +	if (can_fill_pool()) {
> Would have been nice to have this as two patches: first one
> factors out the check into can_fill_pool() without changing the
> logic, while the second one applies the fix to can_fill_pool().

OK, I will send a v6 patch as suggested. However, Thomas had merged the 
v5 patch into tip. I am fine whether it will be one patch or 2 as long 
as the problem is going to be fixed.

Cheers,
Longman