Re: [PATCH] hid: fix bug destroying hidraw device files after parent

["Fernando Luis Vázquez Cao" <fernando_b1@lab.ntt.co.jp>]

I forgot to mention that if the fix below is acceptable it
should be queued for 3.13-stable (older kernels are not
affected).

On 02/26/2014 04:51 PM, Fernando Luis Vázquez Cao wrote:
> I noticed that after hot unplugging a Logitech unifying receiver
> (drivers/hid/hid-logitech-dj.c) the kernel would occasionally spew a
> stack trace similar to this:
>
> usb 1-1.1.2: USB disconnect, device number 7
> WARNING: CPU: 0 PID: 2865 at fs/sysfs/group.c:216 device_del+0x40/0x1b0()
> sysfs group ffffffff8187fa20 not found for kobject 'hidraw0'
> [...]
> CPU: 0 PID: 2865 Comm: upowerd Tainted: G        W 3.14.0-rc4 #7
> Hardware name: LENOVO 7783PN4/        , BIOS 9HKT43AUS 07/11/2011
>   0000000000000009 ffffffff814cd684 ffff880427ccfdf8 ffffffff810616e7
>   ffff88041ec61800 ffff880427ccfe48 ffff88041e444d80 ffff880426fab8e8
>   ffff880429359960 ffffffff8106174c ffffffff81714b98 0000000000000028
> Call Trace:
>   [<ffffffff814cd684>] ? dump_stack+0x41/0x51
>   [<ffffffff810616e7>] ? warn_slowpath_common+0x77/0x90
>   [<ffffffff8106174c>] ? warn_slowpath_fmt+0x4c/0x50
>   [<ffffffff81374fd0>] ? device_del+0x40/0x1b0
>   [<ffffffff8137516f>] ? device_unregister+0x2f/0x50
>   [<ffffffff813751fa>] ? device_destroy+0x3a/0x40
>   [<ffffffffa03ca245>] ? drop_ref+0x55/0x120 [hid]
>   [<ffffffffa03ca3e6>] ? hidraw_release+0x96/0xb0 [hid]
>   [<ffffffff811929da>] ? __fput+0xca/0x210
>   [<ffffffff8107fe17>] ? task_work_run+0x97/0xd0
>   [<ffffffff810139a9>] ? do_notify_resume+0x69/0xa0
>   [<ffffffff814dbd22>] ? int_signal+0x12/0x17
> ---[ end trace 63f4a46f6566d737 ]---
>
> During device removal hid_disconnect() is called via hid_hw_stop() to
> stop the device and free all its resources, including the sysfs
> files. The problem is that if a user space process, such as upowerd,
> holds a reference to a hidraw file the corresponding sysfs files will
> be kept around (drop_ref() does not call device_destroy() if the open
> counter is not 0) and it will be usb_disconnect() who, by calling
> device_del() for the USB device, will indirectly remove the sysfs
> files of the hidraw device (sysfs_remove_dir() is recursive these
> days). Because of this, by the time user space releases the last
> reference to the hidraw file and drop_ref() tries to destroy the
> device the sysfs files are already gone and the kernel will print
> the warning above.
>
> Fix this by calling device_destroy() at USB disconnect time.
>
> Cc: Nestor Lopez Casado <nlopezcasad@logitech.com>
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
> ---
>
> diff -urNp linux-3.14-rc4-orig/drivers/hid/hidraw.c linux-3.14-rc4/drivers/hid/hidraw.c
> --- linux-3.14-rc4-orig/drivers/hid/hidraw.c	2014-02-26 14:21:48.622980475 +0900
> +++ linux-3.14-rc4/drivers/hid/hidraw.c	2014-02-26 14:22:17.990979556 +0900
> @@ -320,13 +320,13 @@ static void drop_ref(struct hidraw *hidr
>   			hid_hw_close(hidraw->hid);
>   			wake_up_interruptible(&hidraw->wait);
>   		}
> +		device_destroy(hidraw_class,
> +			       MKDEV(hidraw_major, hidraw->minor));
>   	} else {
>   		--hidraw->open;
>   	}
>   	if (!hidraw->open) {
>   		if (!hidraw->exist) {
> -			device_destroy(hidraw_class,
> -					MKDEV(hidraw_major, hidraw->minor));
>   			hidraw_table[hidraw->minor] = NULL;
>   			kfree(hidraw);
>   		} else {
>
>
>

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