This is a note to let you know that I've just added the patch titled usb: cdc-wdm: fix reading stuck on device close to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: usb-cdc-wdm-fix-reading-stuck-on-device-close.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 01e01f5c89773c600a9f0b32c888de0146066c3a Mon Sep 17 00:00:00 2001 From: Sergey Ryazanov <ryazanov.s.a@xxxxxxxxx> Date: Sun, 1 May 2022 20:58:28 +0300 Subject: usb: cdc-wdm: fix reading stuck on device close From: Sergey Ryazanov <ryazanov.s.a@xxxxxxxxx> commit 01e01f5c89773c600a9f0b32c888de0146066c3a upstream. cdc-wdm tracks whether a response reading request is in-progress and blocks the next request from being sent until the previous request is completed. As soon as last user closes the cdc-wdm device file, the driver cancels any ongoing requests, resets the pending response counter, but leaves the response reading in-progress flag (WDM_RESPONDING) untouched. So if the user closes the device file during the response receive request is being performed, no more data will be obtained from the modem. The request will be cancelled, effectively preventing the WDM_RESPONDING flag from being reseted. Keeping the flag set will prevent a new response receive request from being sent, permanently blocking the read path. The read path will staying blocked until the module will be reloaded or till the modem will be re-attached. This stuck has been observed with a Huawei E3372 modem attached to an OpenWrt router and using the comgt utility to set up a network connection. Fix this issue by clearing the WDM_RESPONDING flag on the device file close. Without this fix, the device reading stuck can be easily reproduced in a few connection establishing attempts. With this fix, a load test for modem connection re-establishing worked for several hours without any issues. Fixes: 922a5eadd5a3 ("usb: cdc-wdm: Fix race between autosuspend and reading from the device") Signed-off-by: Sergey Ryazanov <ryazanov.s.a@xxxxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> Acked-by: Oliver Neukum <oneukum@xxxxxxxx> Link: https://lore.kernel.org/r/20220501175828.8185-1-ryazanov.s.a@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/usb/class/cdc-wdm.c | 1 + 1 file changed, 1 insertion(+) --- a/drivers/usb/class/cdc-wdm.c +++ b/drivers/usb/class/cdc-wdm.c @@ -744,6 +744,7 @@ static int wdm_release(struct inode *ino kill_urbs(desc); spin_lock_irq(&desc->iuspin); desc->resp_count = 0; + clear_bit(WDM_RESPONDING, &desc->flags); spin_unlock_irq(&desc->iuspin); desc->manage_power(desc->intf, 0); } else { Patches currently in stable-queue which might be from ryazanov.s.a@xxxxxxxxx are queue-4.9/usb-cdc-wdm-fix-reading-stuck-on-device-close.patch