linux-kernel - Re: [PATCH v1] drm/shmem-helper: Fix unsetting shmem vaddr while vmap refcount

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Message-ID: <fwlzp4ib66lqb5c4y2ifcqqrzoxpc3dcetsrhqn4smedbmlwxd@oiu3xuj7ql7x>
Date: Thu, 3 Apr 2025 12:20:53 -0500
From: Lucas De Marchi <lucas.demarchi@...el.com>
To: Dmitry Osipenko <dmitry.osipenko@...labora.com>
CC: Thomas Zimmermann <tzimmermann@...e.de>, Boris Brezillon
	<boris.brezillon@...labora.com>, <dri-devel@...ts.freedesktop.org>,
	<linux-kernel@...r.kernel.org>, <kernel@...labora.com>
Subject: Re: [PATCH v1] drm/shmem-helper: Fix unsetting shmem vaddr while
 vmap refcount > 0

On Thu, Apr 03, 2025 at 05:26:33PM +0300, Dmitry Osipenko wrote:
>We switched to use refcount_t for vmaps and missed to change the vunmap
>code to properly unset the vmap pointer, which is now cleared while vmap's
>refcount > 0. Clear the cached vmap pointer only when refcounting drops to
>zero to fix the bug.
>
>Fixes: e1fc39a92332 ("drm/shmem-helper: Use refcount_t for vmap_use_count")
>Reported-by: Lucas De Marchi <lucas.demarchi@...el.com>
>Closes: https://lore.kernel.org/dri-devel/20250403105053.788b0f6e@collabora.com/T/#m3dca6d81bedc8d6146a56b82694624fbc6fa4c96
>Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>


Tested-by: Lucas De Marchi <lucas.demarchi@...el.com>

this fixes it for me when using `qemu ... -device cirrus-vga`

thanks
Lucas De Marchi