linux-kernel - Re: [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device

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Message-ID: <20190815001137.GE11200@ziepe.ca>
Date:   Wed, 14 Aug 2019 21:11:37 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Matthew Wilcox <willy@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 5/5] mm/hmm: WARN on illegal ->sync_cpu_device_pagetables
 errors

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@...pe.ca>
> Cc: Ralph Campbell <rcampbell@...dia.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Dan Carpenter <dan.carpenter@...cle.com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Balbir Singh <bsingharora@...il.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Souptick Joarder <jrdr.linux@...il.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: linux-mm@...ck.org
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
>  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