Re: [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device_pagetables errors

[Jason Gunthorpe]

On Wed, Aug 14, 2019 at 10:20:27PM +0200, Daniel Vetter wrote:
> Similar to the warning in the mmu notifer, warning if an hmm mirror
> callback gets it's blocking vs. nonblocking handling wrong, or if it
> fails with anything else than -EAGAIN.
> 
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Balbir Singh <bsingharora@xxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
>  mm/hmm.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 16b6731a34db..52ac59384268 100644
> +++ b/mm/hmm.c
> @@ -205,6 +205,9 @@ static int hmm_invalidate_range_start(struct mmu_notifier *mn,
>  			ret = -EAGAIN;
>  			break;
>  		}
> +		WARN(ret, "%pS callback failed with %d in %sblockable context\n",
> +		     mirror->ops->sync_cpu_device_pagetables, ret,
> +		     update.blockable ? "" : "non-");
>  	}
>  	up_read(&hmm->mirrors_sem);

Didn't I beat you to this?

	list_for_each_entry(mirror, &hmm->mirrors, list) {
		int rc;

		rc = mirror->ops->sync_cpu_device_pagetables(mirror, &update);
		if (rc) {
			if (WARN_ON(update.blockable || rc != -EAGAIN))
				continue;
			ret = -EAGAIN;
			break;
		}
	}

Thanks,
Jason