linux-kernel - Re: [PATCH] mm: add dummy can_do

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Date:   Tue, 10 Sep 2019 09:10:30 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-rdma@...r.kernel.org, Jason Gunthorpe <jgg@...lanox.com>,
        Bernard Metzler <bmt@...ich.ibm.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: add dummy can_do_mlock() helper

On Mon 09-09-19 22:41:40, Arnd Bergmann wrote:
> On kernels without CONFIG_MMU, we get a link error for the siw
> driver:
> 
> drivers/infiniband/sw/siw/siw_mem.o: In function `siw_umem_get':
> siw_mem.c:(.text+0x4c8): undefined reference to `can_do_mlock'
> 
> This is probably not the only driver that needs the function
> and could otherwise build correctly without CONFIG_MMU, so
> add a dummy variant that always returns false.
> 
> Fixes: 2251334dcac9 ("rdma/siw: application buffer management")
> Suggested-by: Jason Gunthorpe <jgg@...lanox.com>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Makes sense
Acked-by: Michal Hocko <mhocko@...e.com>

but IB on nonMMU? Whut? Is there any HW that actually supports this?
Just wondering...

> ---
>  include/linux/mm.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 66f296181bcc..cc292273e6ba 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1424,7 +1424,11 @@ extern void pagefault_out_of_memory(void);
>  
>  extern void show_free_areas(unsigned int flags, nodemask_t *nodemask);
>  
> +#ifdef CONFIG_MMU
>  extern bool can_do_mlock(void);
> +#else
> +static inline bool can_do_mlock(void) { return false; }
> +#endif
>  extern int user_shm_lock(size_t, struct user_struct *);
>  extern void user_shm_unlock(size_t, struct user_struct *);
>  
> -- 
> 2.20.0
> 

-- 
Michal Hocko
SUSE Labs