Re: [PATCH 2/4] mm, notifier: Prime lockdep

[Jason Gunthorpe]

On Tue, Aug 20, 2019 at 10:19:00AM +0200, Daniel Vetter wrote:
> We want to teach lockdep that mmu notifiers can be called from direct
> reclaim paths, since on many CI systems load might never reach that
> level (e.g. when just running fuzzer or small functional tests).
> 
> Motivated by a discussion with Jason.
> 
> I've put the annotation into mmu_notifier_register since only when we
> have mmu notifiers registered is there any point in teaching lockdep
> about them. Also, we already have a kmalloc(, GFP_KERNEL), so this is
> safe.
> 
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: "Christian KÃnig" <christian.koenig@xxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
>  mm/mmu_notifier.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index d12e3079e7a4..538d3bb87f9b 100644
> +++ b/mm/mmu_notifier.c
> @@ -256,6 +256,13 @@ static int do_mmu_notifier_register(struct mmu_notifier *mn,
>  
>  	BUG_ON(atomic_read(&mm->mm_users) <= 0);
>  
> +	if (IS_ENABLED(CONFIG_LOCKDEP)) {
> +		fs_reclaim_acquire(GFP_KERNEL);
> +		lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
> +		lock_map_release(&__mmu_notifier_invalidate_range_start_map);
> +		fs_reclaim_release(GFP_KERNEL);
> +	}

Lets try it out at least

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>

Jason