linux-kernel - Re: [PATCH v20 00/10] Add generic DRM-shmem memory shrinker (part 1)

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Message-ID: <91ae764f-d82c-4918-9ce9-0ebbc302c03c@collabora.com>
Date: Thu, 3 Apr 2025 17:10:10 +0300
From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
To: Thomas Zimmermann <tzimmermann@...e.de>,
 Lucas De Marchi <lucas.demarchi@...el.com>
Cc: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>,
 Christian König <christian.koenig@....com>,
 Gerd Hoffmann <kraxel@...hat.com>, Qiang Yu <yuq825@...il.com>,
 Steven Price <steven.price@....com>,
 Boris Brezillon <boris.brezillon@...labora.com>,
 Frank Binns <frank.binns@...tec.com>, Matt Coster <matt.coster@...tec.com>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 kernel@...labora.com, chaitanya.kumar.borah@...el.com
Subject: Re: [PATCH v20 00/10] Add generic DRM-shmem memory shrinker (part 1)

On 4/3/25 10:03, Thomas Zimmermann wrote:
> Hi
> 
> Am 03.04.25 um 02:37 schrieb Lucas De Marchi:
>> On Sun, Mar 23, 2025 at 12:25:58AM +0300, Dmitry Osipenko wrote:
>>> Hi,
>>>
>>> This a continuation of a year-old series that adds generic DRM-shmem
>>> shrinker [1]. The old series became too big with too many patches, more
>>> reasonable to split it up into multiple smaller patchsets. Here is
>>> the firtst part that makes preparatory DRM changes.
>>>
>>> [1] https://lore.kernel.org/dri-devel/20240105184624.508603-1-
>>> dmitry.osipenko@...labora.com/
>>
>> After these patches got merged I started seeing this on ast driver
>> and a similar one qemu-cirrus:
> 
> Same here with simpledrm. I wanted to bisect today.

I've reproduced using bochs drv, it's the last patch "drm/shmem-helper:
Use refcount_t for vmap_use_count" causing the issue. Thanks for the report!

This change fixes it, let me send a proper patch:

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 2d924d547a51..554f1d4c1a76 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -416,10 +416,10 @@ void drm_gem_shmem_vunmap_locked(struct
drm_gem_shmem_object *shmem,
                if (refcount_dec_and_test(&shmem->vmap_use_count)) {
                        vunmap(shmem->vaddr);
                        drm_gem_shmem_unpin_locked(shmem);
+
+                       shmem->vaddr = NULL;
                }
        }
-
-       shmem->vaddr = NULL;
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_vunmap_locked);

-- 
Best regards,
Dmitry