[PATCH 0/4] use mmgrab

[PATCH 0/4] use mmgrab

[Julia Lawall]

Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
helper") and most of the kernel was updated to use it. Update a few
remaining files.

---

 arch/openrisc/kernel/smp.c          |    2 +-
 drivers/misc/cxl/context.c          |    2 +-
 drivers/vfio/pci/vfio_pci_nvlink2.c |    2 +-
 drivers/vfio/vfio_iommu_spapr_tce.c |    2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

[PATCH 1/4] misc: cxl: use mmgrab

[Julia Lawall]

Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
helper") and most of the kernel was updated to use it. Update a
remaining file.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@ expression e; @@
- atomic_inc(&e->mm_count);
+ mmgrab(e);
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

---
 drivers/misc/cxl/context.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c
index aed9c445d1e2..fb2eff69e449 100644
--- a/drivers/misc/cxl/context.c
+++ b/drivers/misc/cxl/context.c
@@ -352,7 +352,7 @@ void cxl_context_free(struct cxl_context *ctx)
 void cxl_context_mm_count_get(struct cxl_context *ctx)
 {
 	if (ctx->mm)
-		atomic_inc(&ctx->mm->mm_count);
+		mmgrab(ctx->mm);
 }
 
 void cxl_context_mm_count_put(struct cxl_context *ctx)

[PATCH 2/4] vfio: vfio_pci_nvlink2: use mmgrab

[Julia Lawall]

Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
helper") and most of the kernel was updated to use it. Update a
remaining file.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@ expression e; @@
- atomic_inc(&e->mm_count);
+ mmgrab(e);
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

---
 drivers/vfio/pci/vfio_pci_nvlink2.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_nvlink2.c b/drivers/vfio/pci/vfio_pci_nvlink2.c
index f2983f0f84be..43df10af7f66 100644
--- a/drivers/vfio/pci/vfio_pci_nvlink2.c
+++ b/drivers/vfio/pci/vfio_pci_nvlink2.c
@@ -159,7 +159,7 @@ static int vfio_pci_nvgpu_mmap(struct vfio_pci_device *vdev,
 	data->useraddr = vma->vm_start;
 	data->mm = current->mm;
 
-	atomic_inc(&data->mm->mm_count);
+	mmgrab(data->mm);
 	ret = (int) mm_iommu_newdev(data->mm, data->useraddr,
 			vma_pages(vma), data->gpu_hpa, &data->mem);
 

[PATCH 3/4] vfio/spapr_tce: use mmgrab

[Julia Lawall]

Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
helper") and most of the kernel was updated to use it. Update a
remaining file.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@ expression e; @@
- atomic_inc(&e->mm_count);
+ mmgrab(e);
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

---
 drivers/vfio/vfio_iommu_spapr_tce.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 26cef65b41e7..16b3adc508db 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -79,7 +79,7 @@ static long tce_iommu_mm_set(struct tce_container *container)
 	}
 	BUG_ON(!current->mm);
 	container->mm = current->mm;
-	atomic_inc(&container->mm->mm_count);
+	mmgrab(container->mm);
 
 	return 0;
 }

[PATCH 4/4] openrisc: use mmgrab

[Julia Lawall]

Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
helper") and most of the kernel was updated to use it. Update a
remaining file.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@ expression e; @@
- atomic_inc(&e->mm_count);
+ mmgrab(e);
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

---
I was not able to compile this file.

 arch/openrisc/kernel/smp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/openrisc/kernel/smp.c b/arch/openrisc/kernel/smp.c
index 7d518ee8bddc..7bd6e0fc7a6d 100644
--- a/arch/openrisc/kernel/smp.c
+++ b/arch/openrisc/kernel/smp.c
@@ -113,7 +113,7 @@ asmlinkage __init void secondary_start_kernel(void)
 	 * All kernel threads share the same mm context; grab a
 	 * reference and switch to it.
 	 */
-	atomic_inc(&mm->mm_count);
+	mmgrab(mm);
 	current->active_mm = mm;
 	cpumask_set_cpu(cpu, mm_cpumask(mm));
 

Re: [PATCH 1/4] misc: cxl: use mmgrab

[Andrew Donnellan]

On 30/12/19 2:42 am, Julia Lawall wrote:
> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a
> remaining file.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> <smpl>
> @@ expression e; @@
> - atomic_inc(&e->mm_count);
> + mmgrab(e);
> </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

Thanks!

Acked-by: Andrew Donnellan <ajd@linux.ibm.com>

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd@linux.ibm.com             IBM Australia Limited

Re: [PATCH 4/4] openrisc: use mmgrab

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 2554 bytes --]

Hi Julia,

I love your patch! Yet something to improve:

[auto build test ERROR on vfio/next]
[also build test ERROR on char-misc/char-misc-testing v5.5-rc3 next-20191220]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Julia-Lawall/use-mmgrab/20191230-011611
base:   https://github.com/awilliam/linux-vfio.git next
config: openrisc-simple_smp_defconfig (attached as .config)
compiler: or1k-linux-gcc (GCC) 9.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=9.2.0 make.cross ARCH=openrisc 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   arch/openrisc/kernel/smp.c: In function 'secondary_start_kernel':
>> arch/openrisc/kernel/smp.c:116:2: error: implicit declaration of function 'mmgrab'; did you mean 'igrab'? [-Werror=implicit-function-declaration]
     116 |  mmgrab(mm);
         |  ^~~~~~
         |  igrab
   cc1: some warnings being treated as errors

vim +116 arch/openrisc/kernel/smp.c

   107	
   108	asmlinkage __init void secondary_start_kernel(void)
   109	{
   110		struct mm_struct *mm = &init_mm;
   111		unsigned int cpu = smp_processor_id();
   112		/*
   113		 * All kernel threads share the same mm context; grab a
   114		 * reference and switch to it.
   115		 */
 > 116		mmgrab(mm);
   117		current->active_mm = mm;
   118		cpumask_set_cpu(cpu, mm_cpumask(mm));
   119	
   120		pr_info("CPU%u: Booted secondary processor\n", cpu);
   121	
   122		setup_cpuinfo();
   123		openrisc_clockevent_init();
   124	
   125		notify_cpu_starting(cpu);
   126	
   127		/*
   128		 * OK, now it's safe to let the boot CPU continue
   129		 */
   130		complete(&cpu_running);
   131	
   132		synchronise_count_slave(cpu);
   133		set_cpu_online(cpu, true);
   134	
   135		local_irq_enable();
   136	
   137		preempt_disable();
   138		/*
   139		 * OK, it's off to the idle thread for us
   140		 */
   141		cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
   142	}
   143	

---
0-DAY kernel test infrastructure                 Open Source Technology Center
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 7983 bytes --]

Re: [PATCH 0/4] use mmgrab

[Dan Carpenter]

On Sun, Dec 29, 2019 at 04:42:54PM +0100, Julia Lawall wrote:
> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a few
> remaining files.

I wonder if there is an automatic way to generate these kind of
Coccinelle scripts which use inlines instead of open coding.  Like maybe
make a list of one line functions, and then auto generate a recipe.  Or
the mmgrab() function could have multiple lines if the first few were
just sanity checks for NULL or something...

regards,
dan carpenter

Re: [PATCH 0/4] use mmgrab

[Julia Lawall]

On Fri, 3 Jan 2020, Dan Carpenter wrote:

> On Sun, Dec 29, 2019 at 04:42:54PM +0100, Julia Lawall wrote:
> > Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> > helper") and most of the kernel was updated to use it. Update a few
> > remaining files.
>
> I wonder if there is an automatic way to generate these kind of
> Coccinelle scripts which use inlines instead of open coding.  Like maybe
> make a list of one line functions, and then auto generate a recipe.  Or
> the mmgrab() function could have multiple lines if the first few were
> just sanity checks for NULL or something...

I tried this at one point (10 years ago!):

https://pages.lip6.fr/Julia.Lawall/acp4is09-lawall.pdf

Perhaps it is worth reviving.

julia

Re: [PATCH 4/4] openrisc: use mmgrab

[Stafford Horne]

On Mon, Dec 30, 2019 at 12:49:19PM +0800, kbuild test robot wrote:
> Hi Julia,
> 
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on vfio/next]
> [also build test ERROR on char-misc/char-misc-testing v5.5-rc3 next-20191220]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
> 
> url:    https://github.com/0day-ci/linux/commits/Julia-Lawall/use-mmgrab/20191230-011611
> base:   https://github.com/awilliam/linux-vfio.git next
> config: openrisc-simple_smp_defconfig (attached as .config)
> compiler: or1k-linux-gcc (GCC) 9.2.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         GCC_VERSION=9.2.0 make.cross ARCH=openrisc 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@intel.com>
> 
> All errors (new ones prefixed by >>):
> 
>    arch/openrisc/kernel/smp.c: In function 'secondary_start_kernel':
> >> arch/openrisc/kernel/smp.c:116:2: error: implicit declaration of function 'mmgrab'; did you mean 'igrab'? [-Werror=implicit-function-declaration]
>      116 |  mmgrab(mm);
>          |  ^~~~~~
>          |  igrab
>    cc1: some warnings being treated as errors

Hi Julia,

It looks like this is just an include issue, do you want to revise the patch?

Once fixed, how do you plan to get this patch series merged?  I can add the
OpenRISC part to my queue or do you have a cleanups queue you can manage?

-Stafford

Re: [PATCH 2/4] vfio: vfio_pci_nvlink2: use mmgrab

[Alex Williamson]

On Sun, 29 Dec 2019 16:42:56 +0100
Julia Lawall <Julia.Lawall@inria.fr> wrote:

> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a
> remaining file.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> <smpl>
> @@ expression e; @@
> - atomic_inc(&e->mm_count);
> + mmgrab(e);
> </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> 
> ---
>  drivers/vfio/pci/vfio_pci_nvlink2.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_nvlink2.c b/drivers/vfio/pci/vfio_pci_nvlink2.c
> index f2983f0f84be..43df10af7f66 100644
> --- a/drivers/vfio/pci/vfio_pci_nvlink2.c
> +++ b/drivers/vfio/pci/vfio_pci_nvlink2.c
> @@ -159,7 +159,7 @@ static int vfio_pci_nvgpu_mmap(struct vfio_pci_device *vdev,
>  	data->useraddr = vma->vm_start;
>  	data->mm = current->mm;
>  
> -	atomic_inc(&data->mm->mm_count);
> +	mmgrab(data->mm);
>  	ret = (int) mm_iommu_newdev(data->mm, data->useraddr,
>  			vma_pages(vma), data->gpu_hpa, &data->mem);
>  
> 

Acked-by: Alex Williamson <alex.williamson@redhat.com>

Thanks!  I'm assuming these will be routed via janitors tree, please
let me know if you intend me to grab these two vfio patches from the
series.  Thanks,

Alex

Re: [PATCH 3/4] vfio/spapr_tce: use mmgrab

[Alex Williamson]

On Sun, 29 Dec 2019 16:42:57 +0100
Julia Lawall <Julia.Lawall@inria.fr> wrote:

> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a
> remaining file.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> <smpl>
> @@ expression e; @@
> - atomic_inc(&e->mm_count);
> + mmgrab(e);
> </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> 
> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 26cef65b41e7..16b3adc508db 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -79,7 +79,7 @@ static long tce_iommu_mm_set(struct tce_container *container)
>  	}
>  	BUG_ON(!current->mm);
>  	container->mm = current->mm;
> -	atomic_inc(&container->mm->mm_count);
> +	mmgrab(container->mm);
>  
>  	return 0;
>  }
> 

Acked-by: Alex Williamson <alex.williamson@redhat.com>

Re: [PATCH 2/4] vfio: vfio_pci_nvlink2: use mmgrab

[Dan Carpenter]

On Mon, Jan 06, 2020 at 04:05:05PM -0700, Alex Williamson wrote:
> 
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
> 
> Thanks!  I'm assuming these will be routed via janitors tree, please
> let me know if you intend me to grab these two vfio patches from the
> series.  Thanks,

There isn't a janitors tree.

regards,
dan carpenter

Re: [PATCH 2/4] vfio: vfio_pci_nvlink2: use mmgrab

[Cornelia Huck]

On Sun, 29 Dec 2019 16:42:56 +0100
Julia Lawall <Julia.Lawall@inria.fr> wrote:

> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a
> remaining file.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> <smpl>
> @@ expression e; @@
> - atomic_inc(&e->mm_count);
> + mmgrab(e);
> </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> 
> ---
>  drivers/vfio/pci/vfio_pci_nvlink2.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Re: [PATCH 3/4] vfio/spapr_tce: use mmgrab

[Cornelia Huck]

On Sun, 29 Dec 2019 16:42:57 +0100
Julia Lawall <Julia.Lawall@inria.fr> wrote:

> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a
> remaining file.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> <smpl>
> @@ expression e; @@
> - atomic_inc(&e->mm_count);
> + mmgrab(e);
> </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> 
> ---
>  drivers/vfio/vfio_iommu_spapr_tce.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Re: [PATCH 2/4] vfio: vfio_pci_nvlink2: use mmgrab

[Julia Lawall]

On Mon, 6 Jan 2020, Alex Williamson wrote:

> On Sun, 29 Dec 2019 16:42:56 +0100
> Julia Lawall <Julia.Lawall@inria.fr> wrote:
>
> > Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> > helper") and most of the kernel was updated to use it. Update a
> > remaining file.
> >
> > The semantic patch that makes this change is as follows:
> > (http://coccinelle.lip6.fr/)
> >
> > <smpl>
> > @@ expression e; @@
> > - atomic_inc(&e->mm_count);
> > + mmgrab(e);
> > </smpl>
> >
> > Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> >
> > ---
> >  drivers/vfio/pci/vfio_pci_nvlink2.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/vfio/pci/vfio_pci_nvlink2.c b/drivers/vfio/pci/vfio_pci_nvlink2.c
> > index f2983f0f84be..43df10af7f66 100644
> > --- a/drivers/vfio/pci/vfio_pci_nvlink2.c
> > +++ b/drivers/vfio/pci/vfio_pci_nvlink2.c
> > @@ -159,7 +159,7 @@ static int vfio_pci_nvgpu_mmap(struct vfio_pci_device *vdev,
> >  	data->useraddr = vma->vm_start;
> >  	data->mm = current->mm;
> >
> > -	atomic_inc(&data->mm->mm_count);
> > +	mmgrab(data->mm);
> >  	ret = (int) mm_iommu_newdev(data->mm, data->useraddr,
> >  			vma_pages(vma), data->gpu_hpa, &data->mem);
> >
> >
>
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
>
> Thanks!  I'm assuming these will be routed via janitors tree, please
> let me know if you intend me to grab these two vfio patches from the
> series.  Thanks,

Please take them directly.

thanks,
julia

Re: [PATCH 2/4] vfio: vfio_pci_nvlink2: use mmgrab

[Alex Williamson]

On Tue, 7 Jan 2020 18:00:31 +0100 (CET)
Julia Lawall <julia.lawall@inria.fr> wrote:

> On Mon, 6 Jan 2020, Alex Williamson wrote:
> 
> > On Sun, 29 Dec 2019 16:42:56 +0100
> > Julia Lawall <Julia.Lawall@inria.fr> wrote:
> >  
> > > Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> > > helper") and most of the kernel was updated to use it. Update a
> > > remaining file.
> > >
> > > The semantic patch that makes this change is as follows:
> > > (http://coccinelle.lip6.fr/)
> > >
> > > <smpl>
> > > @@ expression e; @@
> > > - atomic_inc(&e->mm_count);
> > > + mmgrab(e);
> > > </smpl>
> > >
> > > Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
> > >
> > > ---
> > >  drivers/vfio/pci/vfio_pci_nvlink2.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/vfio/pci/vfio_pci_nvlink2.c b/drivers/vfio/pci/vfio_pci_nvlink2.c
> > > index f2983f0f84be..43df10af7f66 100644
> > > --- a/drivers/vfio/pci/vfio_pci_nvlink2.c
> > > +++ b/drivers/vfio/pci/vfio_pci_nvlink2.c
> > > @@ -159,7 +159,7 @@ static int vfio_pci_nvgpu_mmap(struct vfio_pci_device *vdev,
> > >  	data->useraddr = vma->vm_start;
> > >  	data->mm = current->mm;
> > >
> > > -	atomic_inc(&data->mm->mm_count);
> > > +	mmgrab(data->mm);
> > >  	ret = (int) mm_iommu_newdev(data->mm, data->useraddr,
> > >  			vma_pages(vma), data->gpu_hpa, &data->mem);
> > >
> > >  
> >
> > Acked-by: Alex Williamson <alex.williamson@redhat.com>
> >
> > Thanks!  I'm assuming these will be routed via janitors tree, please
> > let me know if you intend me to grab these two vfio patches from the
> > series.  Thanks,  
> 
> Please take them directly.

Ok, I'll queue patches 2 & 3 for v5.6.  Thanks,

Alex

Re: [PATCH 1/4] misc: cxl: use mmgrab

[Michael Ellerman]

On Sun, 2019-12-29 at 15:42:55 UTC, Julia Lawall wrote:
> Mmgrab was introduced in commit f1f1007644ff ("mm: add new mmgrab()
> helper") and most of the kernel was updated to use it. Update a
> remaining file.
> 
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
> 
> <smpl>
> @@ expression e; @@
> - atomic_inc(&e->mm_count);
> + mmgrab(e);
> </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/30e813cf46ccaeea6508607632e49b4a1d743d2a

cheers

Re: [PATCH 4/4] openrisc: use mmgrab

[Stafford Horne]

On Mon, Dec 30, 2019 at 12:49:19PM +0800, kbuild test robot wrote:
> Hi Julia,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on vfio/next]
> [also build test ERROR on char-misc/char-misc-testing v5.5-rc3 next-20191220]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
> 
> url:    https://github.com/0day-ci/linux/commits/Julia-Lawall/use-mmgrab/20191230-011611
> base:   https://github.com/awilliam/linux-vfio.git next
> config: openrisc-simple_smp_defconfig (attached as .config)
> compiler: or1k-linux-gcc (GCC) 9.2.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         GCC_VERSION=9.2.0 make.cross ARCH=openrisc 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@intel.com>
> 
> All errors (new ones prefixed by >>):
> 
>    arch/openrisc/kernel/smp.c: In function 'secondary_start_kernel':
> >> arch/openrisc/kernel/smp.c:116:2: error: implicit declaration of function 'mmgrab'; did you mean 'igrab'? [-Werror=implicit-function-declaration]
>      116 |  mmgrab(mm);
>          |  ^~~~~~
>          |  igrab
>    cc1: some warnings being treated as errors
> 
> vim +116 arch/openrisc/kernel/smp.c
> 
>    107	
>    108	asmlinkage __init void secondary_start_kernel(void)
>    109	{
>    110		struct mm_struct *mm = &init_mm;
>    111		unsigned int cpu = smp_processor_id();
>    112		/*
>    113		 * All kernel threads share the same mm context; grab a
>    114		 * reference and switch to it.
>    115		 */
>  > 116		mmgrab(mm);
>    117		current->active_mm = mm;
>    118		cpumask_set_cpu(cpu, mm_cpumask(mm));
>    119	
>    120		pr_info("CPU%u: Booted secondary processor\n", cpu);
>    121	
>    122		setup_cpuinfo();
>    123		openrisc_clockevent_init();
>    124	
>    125		notify_cpu_starting(cpu);
>    126	
>    127		/*
>    128		 * OK, now it's safe to let the boot CPU continue
>    129		 */
>    130		complete(&cpu_running);
>    131	
>    132		synchronise_count_slave(cpu);
>    133		set_cpu_online(cpu, true);
>    134	
>    135		local_irq_enable();
>    136	
>    137		preempt_disable();
>    138		/*
>    139		 * OK, it's off to the idle thread for us
>    140		 */
>    141		cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
>    142	}
>    143	
> 

Hello,  FYI I have fixed this commit and queued it on my 5.7 branch.

-Stafford