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 my usb git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From 01e01f5c89773c600a9f0b32c888de0146066c3a Mon Sep 17 00:00:00 2001 From: Sergey Ryazanov ryazanov.s.a@gmail.com Date: Sun, 1 May 2022 20:58:28 +0300 Subject: usb: cdc-wdm: fix reading stuck on device close

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@gmail.com Cc: stable stable@vger.kernel.org Acked-by: Oliver Neukum oneukum@suse.com Link: https://lore.kernel.org/r/20220501175828.8185-1-ryazanov.s.a@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/class/cdc-wdm.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c index 7f2c83f299d3..eebe782380fb 100644 --- a/drivers/usb/class/cdc-wdm.c +++ b/drivers/usb/class/cdc-wdm.c @@ -774,6 +774,7 @@ static int wdm_release(struct inode *inode, struct file *file) poison_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); unpoison_urbs(desc);