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From:   Oleksandr Natalenko <oleksandr@natalenko.name>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andi Shyti <andi.shyti@linux.intel.com>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Matthew Auld <matthew.auld@intel.com>,
        Matt Roper <matthew.d.roper@intel.com>,
        Aravind Iddamsetty <aravind.iddamsetty@intel.com>,
        Fei Yang <fei.yang@intel.com>,
        Thomas =?ISO-8859-1?Q?Hellstr=F6m?= 
        <thomas.hellstrom@linux.intel.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Chris Wilson <chris@chris-wilson.co.uk>,
        Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org
Subject: Re: [REGRESSION] [BISECTED] Panic in gen8_ggtt_insert_entries() with v6.5
Date:   Tue, 19 Sep 2023 20:11:47 +0200
Message-ID: <2554845.iZASKD2KPV@natalenko.name>
In-Reply-To: <ZQnBrLCPnZfG0A1s@casper.infradead.org>
References: <4857570.31r3eYUQgx@natalenko.name> <6287208.lOV4Wx5bFT@natalenko.name>
 <ZQnBrLCPnZfG0A1s@casper.infradead.org>
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From: Oleksandr Natalenko <oleksandr@natalenko.name>
To: Matthew Wilcox <willy@infradead.org>
Date: Tue, 19 Sep 2023 20:11:47 +0200
Message-ID: <2554845.iZASKD2KPV@natalenko.name>
In-Reply-To: <ZQnBrLCPnZfG0A1s@casper.infradead.org>
MIME-Version: 1.0

Hello.

On =C3=BAter=C3=BD 19. z=C3=A1=C5=99=C3=AD 2023 17:43:40 CEST Matthew Wilco=
x wrote:
> On Tue, Sep 19, 2023 at 10:26:42AM +0200, Oleksandr Natalenko wrote:
> > Andrzej asked me to try to revert commits 0b62af28f249, e0b72c14d8dc an=
d 1e0877d58b1e, and reverting those fixed the i915 crash for me. The e0b72c=
14d8dc and 1e0877d58b1e commits look like just prerequisites, so I assume 0=
b62af28f249 ("i915: convert shmem_sg_free_table() to use a folio_batch") is=
 the culprit here.
> >=20
> > Could you please check this?
> >=20
> > Our conversation with Andrzej is available at drm-intel GitLab [1].
> >=20
> > Thanks.
> >=20
> > [1] https://gitlab.freedesktop.org/drm/intel/-/issues/9256
>=20
> Wow, that is some great debugging.  Thanks for all the time & effort
> you and others have invested.  Sorry for breaking your system.
>=20
> You're almost right about the "prerequisites", but it's in the other
> direction; 0b62af28f249 is a prerequisite for the later two cleanups,
> so reverting all three is necessary to test 0b62af28f249.
>=20
> It seems to me that you've isolated the problem to constructing overly
> long sg lists.  I didn't realise that was going to be a problem, so
> that's my fault.
>=20
> Could I ask you to try this patch?  I'll follow up with another patch
> later because I think I made another assumption that may not be valid.

I can confirm this one fixes the issue for me on T460s laptop. Thank you!

Should you submit it, please add:

=46ixes: 0b62af28f2 ("i915: convert shmem_sg_free_table() to use a folio_ba=
tch")
Cc: stable@vger.kernel.org # 6.5.x
Link: https://gitlab.freedesktop.org/drm/intel/-/issues/9256
Link: https://lore.kernel.org/lkml/6287208.lOV4Wx5bFT@natalenko.name/
Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>

> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/=
i915/gem/i915_gem_shmem.c
> index 8f1633c3fb93..73a4a4eb29e0 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> @@ -100,6 +100,7 @@ int shmem_sg_alloc_table(struct drm_i915_private *i91=
5, struct sg_table *st,
>  	st->nents =3D 0;
>  	for (i =3D 0; i < page_count; i++) {
>  		struct folio *folio;
> +		unsigned long nr_pages;
>  		const unsigned int shrink[] =3D {
>  			I915_SHRINK_BOUND | I915_SHRINK_UNBOUND,
>  			0,
> @@ -150,6 +151,8 @@ int shmem_sg_alloc_table(struct drm_i915_private *i91=
5, struct sg_table *st,
>  			}
>  		} while (1);
> =20
> +		nr_pages =3D min_t(unsigned long,
> +				folio_nr_pages(folio), page_count - i);
>  		if (!i ||
>  		    sg->length >=3D max_segment ||
>  		    folio_pfn(folio) !=3D next_pfn) {
> @@ -157,13 +160,13 @@ int shmem_sg_alloc_table(struct drm_i915_private *i=
915, struct sg_table *st,
>  				sg =3D sg_next(sg);
> =20
>  			st->nents++;
> -			sg_set_folio(sg, folio, folio_size(folio), 0);
> +			sg_set_folio(sg, folio, nr_pages * PAGE_SIZE, 0);
>  		} else {
>  			/* XXX: could overflow? */
> -			sg->length +=3D folio_size(folio);
> +			sg->length +=3D nr_pages * PAGE_SIZE;
>  		}
> -		next_pfn =3D folio_pfn(folio) + folio_nr_pages(folio);
> -		i +=3D folio_nr_pages(folio) - 1;
> +		next_pfn =3D folio_pfn(folio) + nr_pages;
> +		i +=3D nr_pages - 1;
> =20
>  		/* Check that the i965g/gm workaround works. */
>  		GEM_BUG_ON(gfp & __GFP_DMA32 && next_pfn >=3D 0x00100000UL);

=2D-=20
Oleksandr Natalenko (post-factum)
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