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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>,
        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
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From:   Laurent Dufour <ldufour@linux.vnet.ibm.com>
Date:   Wed, 4 Apr 2018 12:19:48 +0200
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On 04/04/2018 02:48, David Rientjes wrote:
> On Wed, 28 Mar 2018, Laurent Dufour wrote:
> 
>> On 26/03/2018 00:10, David Rientjes wrote:
>>> On Wed, 21 Mar 2018, Laurent Dufour 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)

No, this not needed because the vma is allocated with kmem_cache_zalloc() so
vm_ref_count is 0, and insert_vm_struc() will later call
__vma_link_rb() which will call seqcount_init().

Furhtermore, in case of error, the vma structure is freed without calling
get_vma() so there is risk of lockdep warning.