linux-kernel - Re: [PATCH] rdma/siw: fix NOMMU build

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Date:   Sat, 7 Sep 2019 07:34:46 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Bernard Metzler <bmt@...ich.ibm.com>,
        Doug Ledford <dledford@...hat.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        John Hubbard <jhubbard@...dia.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rdma/siw: fix NOMMU build

On Fri, Sep 06, 2019 at 05:10:10PM +0200, 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'
> 
> I don't know whether this driver is able to work at all without
> an MMU, but it's easy to avoid the link problem by adding another
> compile-time check.
> 
> Fixes: 2251334dcac9 ("rdma/siw: application buffer management")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>  drivers/infiniband/sw/siw/siw_mem.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
> index e99983f07663..b3b614c07fdb 100644
> +++ b/drivers/infiniband/sw/siw/siw_mem.c
> @@ -374,7 +374,7 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
>  	unsigned int foll_flags = FOLL_WRITE;
>  	int num_pages, num_chunks, i, rv = 0;
>  
> -	if (!can_do_mlock())
> +	if (!IS_ENABLED(CONFIG_MMU) || !can_do_mlock())
>  		return ERR_PTR(-EPERM);

I feel like !CONFIG_MMU should provide a dummy inline stub for can_do_mlock
instead?

Jason