linux-kernel - Re: [mm] b1f0502d04: INFO:trying_to_register_non-static

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Date:   Wed, 4 Apr 2018 12:19:48 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     kernel test robot <fengguang.wu@...el.com>,
        paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
        akpm@...ux-foundation.org, kirill@...temov.name,
        ak@...ux.intel.com, mhocko@...nel.org, dave@...olabs.net,
        jack@...e.cz, Matthew Wilcox <willy@...radead.org>,
        benh@...nel.crashing.org, mpe@...erman.id.au, paulus@...ba.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, hpa@...or.com,
        Will Deacon <will.deacon@....com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        kemi.wang@...el.com, sergey.senozhatsky.work@...il.com,
        Daniel Jordan <daniel.m.jordan@...cle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        haren@...ux.vnet.ibm.com, khandual@...ux.vnet.ibm.com,
        npiggin@...il.com, bsingharora@...il.com,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        linuxppc-dev@...ts.ozlabs.org, x86@...nel.org, lkp@...org
Subject: Re: [mm] b1f0502d04: INFO:trying_to_register_non-static_key



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.