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@redhat.com Cc: stable@vger.kernel.org

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