Hi,
On Sunday, June 03, 2018 11:46:29 AM Mikulas Patocka wrote:
> I have a USB display adapter using the udlfb driver and I use it on an ARM
> board that doesn't have any graphics card. When I plug the adapter in, the
> console is properly displayed, however when I unplug and re-plug the
> adapter, the console is not displayed and I can't access it until I reboot
> the board.
>
> The reason is this:
> When the adapter is unplugged, dlfb_usb_disconnect calls
> unlink_framebuffer, then it waits until the reference count drops to zero
> and then it deallocates the framebuffer. However, the console that is
> attached to the framebuffer device keeps the reference count non-zero, so
> the framebuffer device is never destroyed. When the USB adapter is plugged
> again, it creates a new device /dev/fb1 and the console is not attached to
> it.
>
> This patch fixes the bug by unbinding the console from unlink_framebuffer.
> The code to unbind the console is moved from do_unregister_framebuffer to
> a function unbind_console. When the console is unbound, the reference
> count drops to zero and the udlfb driver frees the framebuffer. When the
> adapter is plugged back, a new framebuffer is created and the console is
> attached to it.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
After this change unbind_console() will be called twice in the standard
framebuffer unregister path:
- first time, directly by do_unregister_framebuffer()
- second time, indirectly by do_unregister_framebuffer()->unlink_framebuffer()
This doesn't look correctly.
Also why can't udlfb just use unregister_framebuffer() like all other
drivers (it uses unlink_framebuffer() and it is the only user of this
helper)?
> ---
> drivers/video/fbdev/core/fbmem.c | 21 +++++++++++++++++----
> 1 file changed, 17 insertions(+), 4 deletions(-)
>
> Index: linux-4.16.12/drivers/video/fbdev/core/fbmem.c
> ===================================================================
> --- linux-4.16.12.orig/drivers/video/fbdev/core/fbmem.c 2018-05-26 06:13:20.000000000 +0200
> +++ linux-4.16.12/drivers/video/fbdev/core/fbmem.c 2018-05-26 06:13:20.000000000 +0200
> @@ -1805,12 +1805,12 @@ static int do_register_framebuffer(struc
> return 0;
> }
>
> -static int do_unregister_framebuffer(struct fb_info *fb_info)
> +static int unbind_console(struct fb_info *fb_info)
> {
> struct fb_event event;
> - int i, ret = 0;
> + int ret;
> + int i = fb_info->node;
>
> - i = fb_info->node;
> if (i < 0 || i >= FB_MAX || registered_fb[i] != fb_info)
> return -EINVAL;
>
> @@ -1825,6 +1825,16 @@ static int do_unregister_framebuffer(str
> unlock_fb_info(fb_info);
> console_unlock();
>
> + return ret;
> +}
> +
> +static int do_unregister_framebuffer(struct fb_info *fb_info)
> +{
> + struct fb_event event;
> + int ret;
> +
> + ret = unbind_console(fb_info);
> +
> if (ret)
> return -EINVAL;
>
> @@ -1835,7 +1845,7 @@ static int do_unregister_framebuffer(str
> (fb_info->pixmap.flags & FB_PIXMAP_DEFAULT))
> kfree(fb_info->pixmap.addr);
> fb_destroy_modelist(&fb_info->modelist);
> - registered_fb[i] = NULL;
> + registered_fb[fb_info->node] = NULL;
> num_registered_fb--;
> fb_cleanup_device(fb_info);
> event.info = fb_info;
> @@ -1860,6 +1870,9 @@ int unlink_framebuffer(struct fb_info *f
> device_destroy(fb_class, MKDEV(FB_MAJOR, i));
> fb_info->dev = NULL;
> }
> +
> + unbind_console(fb_info);
> +
> return 0;
> }
> EXPORT_SYMBOL(unlink_framebuffer);
Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
