On 2022/11/17 13:20, Zhang, Qiang1 wrote:
>
>
> On 2022/11/16 22:15, Zqiang wrote:
>> Currently, the mem_dump_obj() is invoked in call_rcu(), the
>>
>> Plan to call mem_dump_obj() in rcu_do_batch().
>>
>> call_rcu() is maybe invoked in non-preemptive code segment,
>> for object allocated from vmalloc(), the following scenarios
>> may occur:
>>
>> CPU 0
>> tasks context
>> spin_lock(&vmap_area_lock)
>> Interrupt context
>> call_rcu()
>> mem_dump_obj
>> vmalloc_dump_obj
>> spin_lock(&vmap_area_lock) <--deadlock
>>
>> and for PREEMPT-RT kernel, the spinlock will convert to sleepable
>> lock, it also make vmap_area_lock spinlock can not acquire in
>> non-preemptive code segment. therefore, this commit make the
>> vmalloc_dump_obj() call in a preemptible context.
>>
>> Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
>> ---
>> mm/util.c | 10 +++++++---
>> 1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/util.c b/mm/util.c
>> index 12984e76767e..465f8b8824ca 100644
>> --- a/mm/util.c
>> +++ b/mm/util.c
>> @@ -1124,8 +1124,12 @@ void mem_dump_obj(void *object)
>> return;
>> }
>>
>> - if (vmalloc_dump_obj(object))
>> - return;
>> + if (is_vmalloc_addr(object)) {
>> + if (preemptible() && vmalloc_dump_obj(object))
>>
>> preemptible() --> !in_interrupt()?
>
> Hi Leizhen
>
> !in_interrupt() not include following scenario:
>
> task context:
>
> local_irq_save() or preempt_disable();
> call_rcu()
> mem_dump_obj()
> vmalloc_dump_obj()
> spin_lock(&vmap_area_lock)
> local_irq_restore() or preempt_denable();
>
> for PREEMPT-RT kernel, spinlock will convert to sleepable lock.
OK.
>
>>
>> + return;
>> + type = "vmalloc memory";
>> + goto end;
>> + }
>>
>> Move into vmalloc_dump_obj()?
>
> you mean move preemptible() into vmalloc_dump_obj()?
Move all? Currently, vmalloc_dump_obj() is invoked only by
mem_dump_obj(). The encapsulation is a little better in my opinion.
>
> Thanks
> Zqiang
>
>>
>>
>> if (virt_addr_valid(object))
>> type = "non-slab/vmalloc memory";
>> @@ -1135,7 +1139,7 @@ void mem_dump_obj(void *object)
>> type = "zero-size pointer";
>> else
>> type = "non-paged memory";
>> -
>> +end:
>> pr_cont(" %s\n", type);
>> }
>> EXPORT_SYMBOL_GPL(mem_dump_obj);
>>
>
--
Regards,
Zhen Lei
