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

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Date:   Tue, 15 Nov 2022 10:01:11 +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 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.


> 
> .
> 

-- 
Regards,
  Zhen Lei