Re: [PATCH v2] fbdev: Fix invalid page access after closing deferred I/O devices

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi,

this bug could be a symptom of the problem reported at [1].

Best regards
Thomas

[1] 
https://lore.kernel.org/dri-devel/CAM0jSHOcvZoyv-y6bnvFaUybRQsDx_mfOydL1uaNM4T4PgcA=A@xxxxxxxxxxxxxx/T/#mfbef4df9b49fc5fda9bcfa26db5ca13cdaef6d7e

Am 29.01.23 um 09:28 schrieb Takashi Iwai:
> When a fbdev with deferred I/O is once opened and closed, the dirty
> pages still remain queued in the pageref list, and eventually later
> those may be processed in the delayed work.  This may lead to a
> corruption of pages, hitting an Oops.
>
> This patch makes sure to cancel the delayed work and clean up the
> pageref list at closing the device for addressing the bug.  A part of
> the cleanup code is factored out as a new helper function that is
> called from the common fb_release().
>
> Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
> ---
> v1->v2: Fix build error without CONFIG_FB_DEFERRED_IO
>
>   drivers/video/fbdev/core/fb_defio.c | 10 +++++++++-
>   drivers/video/fbdev/core/fbmem.c    |  4 ++++
>   include/linux/fb.h                  |  1 +
>   3 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
> index c730253ab85c..583cbcf09446 100644
> --- a/drivers/video/fbdev/core/fb_defio.c
> +++ b/drivers/video/fbdev/core/fb_defio.c
> @@ -313,7 +313,7 @@ void fb_deferred_io_open(struct fb_info *info,
>   }
>   EXPORT_SYMBOL_GPL(fb_deferred_io_open);
>   
> -void fb_deferred_io_cleanup(struct fb_info *info)
> +void fb_deferred_io_release(struct fb_info *info)
>   {
>   	struct fb_deferred_io *fbdefio = info->fbdefio;
>   	struct page *page;
> @@ -327,6 +327,14 @@ void fb_deferred_io_cleanup(struct fb_info *info)
>   		page = fb_deferred_io_page(info, i);
>   		page->mapping = NULL;
>   	}
> +}
> +EXPORT_SYMBOL_GPL(fb_deferred_io_release);
> +
> +void fb_deferred_io_cleanup(struct fb_info *info)
> +{
> +	struct fb_deferred_io *fbdefio = info->fbdefio;
> +
> +	fb_deferred_io_release(info);
>   
>   	kvfree(info->pagerefs);
>   	mutex_destroy(&fbdefio->lock);
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 3a6c8458eb8d..ab3545a00abc 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1454,6 +1454,10 @@ __releases(&info->lock)
>   	struct fb_info * const info = file->private_data;
>   
>   	lock_fb_info(info);
> +#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)
> +	if (info->fbdefio)
> +		fb_deferred_io_release(info);
> +#endif
>   	if (info->fbops->fb_release)
>   		info->fbops->fb_release(info,1);
>   	module_put(info->fbops->owner);
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 96b96323e9cb..73eb1f85ea8e 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -662,6 +662,7 @@ extern int  fb_deferred_io_init(struct fb_info *info);
>   extern void fb_deferred_io_open(struct fb_info *info,
>   				struct inode *inode,
>   				struct file *file);
> +extern void fb_deferred_io_release(struct fb_info *info);
>   extern void fb_deferred_io_cleanup(struct fb_info *info);
>   extern int fb_deferred_io_fsync(struct file *file, loff_t start,
>   				loff_t end, int datasync);

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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