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Subject: Re: [mm] b1f0502d04: INFO:trying_to_register_non-static_key
To:     David Rientjes <rientjes@google.com>
Cc:     kernel test robot <fengguang.wu@intel.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
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        Will Deacon <will.deacon@arm.com>,
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        Daniel Jordan <daniel.m.jordan@oracle.com>,
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From:   Laurent Dufour <ldufour@linux.vnet.ibm.com>
Date:   Wed, 4 Apr 2018 12:28:44 +0200
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On 04/04/2018 03:03, David Rientjes wrote:
> On Tue, 3 Apr 2018, David Rientjes wrote:
> 
>>>>> I found the root cause of this lockdep warning.
>>>>>
>>>>> In mmap_region(), unmap_region() may be called while vma_link() has not been
>>>>> called. This happens during the error path if call_mmap() failed.
>>>>>
>>>>> The only to fix that particular case is to call
>>>>> seqcount_init(&vma->vm_sequence) when initializing the vma in mmap_region().
>>>>>
>>>>
>>>> Ack, although that would require a fixup to dup_mmap() as well.
>>>
>>> You're right, I'll fix that too.
>>>
>>
>> I also think the following is needed:
>>
>> diff --git a/fs/exec.c b/fs/exec.c
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -312,6 +312,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
>>  	vma->vm_flags = VM_SOFTDIRTY | VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
>>  	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
>>  	INIT_LIST_HEAD(&vma->anon_vma_chain);
>> +#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
>> +	seqcount_init(&vma->vm_sequence);
>> +	atomic_set(&vma->vm_ref_count, 0);
>> +#endif
>>  
>>  	err = insert_vm_struct(mm, vma);
>>  	if (err)
>>
> 
> Ugh, I think there are a number of other places where this is needed as 
> well in mm/mmap.c.  I think it would be better to just create a new 
> alloc_vma(unsigned long flags) that all vma allocators can use and for 
> CONFIG_SPECULATIVE_PAGE_FAULT will initialize the seqcount_t and atomic_t.
> 

I don't think this is really needed, most of the time the vma structure is
allocated cleared and is then link to rb tree via vma_link.

The only case generating a locked warning is when the vma is referenced in the
error path before being linked in the mm tree and that is not usual.