linux-kernel - Re: [PATCH] mm/vmalloc: allow mem_dump_obj() to be called in interrupt context

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Date:   Wed, 16 Nov 2022 22:05:49 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Zhang Qiang1 <qiang1.zhang@...el.com>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: Re: [PATCH] mm/vmalloc: allow mem_dump_obj() to be called in
 interrupt context



On 2022/11/15 10:01, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/11/15 8:54, Andrew Morton wrote:
>> On Sat, 12 Nov 2022 20:15:37 +0800 Zhen Lei <thunder.leizhen@...wei.com> wrote:
>>
>>> The function mem_dump_obj() can sometimes provide valuable debugging
>>> information, but it cannot be called in an interrupt context because
>>> spinlock vmap_area_lock has not been protected against IRQs. If the
>>> current task has held the lock before hard/soft interrupt handler calls
>>> mem_dump_obj(), simply abandoning the dump operation can avoid deadlock.
>>> That is, no deadlock occurs in extreme cases, and dump succeeds in most
>>> cases.
>>>
>>> ...
>>>
>>> --- a/mm/vmalloc.c
>>> +++ b/mm/vmalloc.c
>>> @@ -4034,6 +4034,9 @@ bool vmalloc_dump_obj(void *object)
>>>  	struct vm_struct *vm;
>>>  	void *objp = (void *)PAGE_ALIGN((unsigned long)object);
>>>  
>>> +	if (unlikely(spin_is_locked(&vmap_area_lock)))
>>> +		return false;
>>> +
>>>  	vm = find_vm_area(objp);
>>>  	if (!vm)
>>>  		return false;
>>
>> Yes, but this will worsen the current uses of this function.  Consider
>> the case where task A wants to call vmalloc_dump_obj() but task B holds
>> vmap_area_lock.  No problem, task A will simply spin until task B is
>> done.
>>
>> But after this patch, task A's call to vmalloc_dump_obj() will return
>> without having done anything.
> 
> Oh, right, this problem occurs when task A and task B run on
> two different cores.

I've rethought it, this can be solved by adding in_interrupt().

> 
> 
>>
>> .
>>
> 

-- 
Regards,
  Zhen Lei