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Subject: Re: [PATCH 2/2] mm: vmalloc: Pass proper vm_start into debugobjects
To:     Chintan Pandya <cpandya@codeaurora.org>, vbabka@suse.cz,
        labbott@redhat.com, catalin.marinas@arm.com, hannes@cmpxchg.org,
        f.fainelli@gmail.com, xieyisheng1@huawei.com,
        ard.biesheuvel@linaro.org, richard.weiyang@gmail.com,
        byungchul.park@lge.com
References: <1523619234-17635-1-git-send-email-cpandya@codeaurora.org>
 <1523619234-17635-3-git-send-email-cpandya@codeaurora.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
From:   Anshuman Khandual <khandual@linux.vnet.ibm.com>
Date:   Fri, 13 Apr 2018 17:31:49 +0530
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On 04/13/2018 05:03 PM, Chintan Pandya wrote:
> Client can call vunmap with some intermediate 'addr'
> which may not be the start of the VM area. Entire
> unmap code works with vm->vm_start which is proper
> but debug object API is called with 'addr'. This
> could be a problem within debug objects.
> 
> Pass proper start address into debug object API.
> 
> Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
> ---
>  mm/vmalloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 9ff21a1..28034c55 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1526,8 +1526,8 @@ static void __vunmap(const void *addr, int deallocate_pages)
>  		return;
>  	}
>  
> -	debug_check_no_locks_freed(addr, get_vm_area_size(area));
> -	debug_check_no_obj_freed(addr, get_vm_area_size(area));
> +	debug_check_no_locks_freed(area->addr, get_vm_area_size(area));
> +	debug_check_no_obj_freed(area->addr, get_vm_area_size(area));

This kind of makes sense to me but I am not sure. We also have another
instance of this inside the function vm_unmap_ram() where we call for
debug on locks without even finding the vmap_area first. But it is true
that in both these functions the vmap_area gets freed eventually. Hence
the entire mapping [va->va_start --> va->va_end] gets unmapped. Sounds
like these debug functions should have the entire range as argument.
But I am not sure and will seek Michal's input on this.