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Date:   Tue, 3 Apr 2018 18:03:22 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Laurent Dufour <ldufour@linux.vnet.ibm.com>
cc:     kernel test robot <fengguang.wu@intel.com>,
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Subject: Re: [mm] b1f0502d04: INFO:trying_to_register_non-static_key
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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.