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Date: Tue, 3 Apr 2018 18:03:22 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
Subject: Re: [mm] b1f0502d04: INFO:trying_to_register_non-static_key
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References: <20180317075119.u6yuem2bhxvggbz3@inn> <792c0f75-7e7f-cd81-44ae-4205f6e4affc@linux.vnet.ibm.com> <alpine.DEB.2.20.1803251510040.80485@chino.kir.corp.google.com> <aa6f2ff1-ff67-106a-e0e4-522ac82a7bf0@linux.vnet.ibm.com>
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To: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: kernel test robot <fengguang.wu@intel.com>, paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox <willy@infradead.org>, benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, hpa@zytor.com, Will Deacon <will.deacon@arm.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Andrea Arcangeli <aarcange@redhat.com>, Alexei Starovoitov <alexei.starovoitov@gmail.com>, kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com, Daniel Jordan <daniel.m.jordan@oracle.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen <tim.c.chen@linux.intel.com>, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, lkp@01.org

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.