[PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

[PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

[Zqiang]

Currently, the mem_dump_obj() is invoked in call_rcu(), the
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@intel.com>
---
 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))
+			return;
+		type = "vmalloc memory";
+		goto end;
+	}
 
 	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);
-- 
2.25.1

Re: [PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

[Leizhen (ThunderTown)]

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@intel.com>
> ---
>  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()?

> +			return;
> +		type = "vmalloc memory";
> +		goto end;
> +	}

Move into vmalloc_dump_obj()?

>  
>  	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

RE: [PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

[Zhang, Qiang1]

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@intel.com>
> ---
>  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.

>
> +			return;
> +		type = "vmalloc memory";
> +		goto end;
> +	}
>
>Move into vmalloc_dump_obj()?

you mean move preemptible() into vmalloc_dump_obj()?

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

Re: [PATCH] rcu: Make vmalloc_dump_obj() call in a preemptible context

[Leizhen (ThunderTown)]

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@intel.com>
>> ---
>>  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