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usb: gadget: u_serial: Avoid spinlock recursion in __gs_console_push

When serial console over USB is enabled, gs_console_connect
queues gs_console_work, where it acquires the spinlock and
queues the usb request, and this request goes to gadget layer.
Now consider a situation where gadget layer prints something
to dmesg, this will eventually call gs_console_write() which
requires cons->lock. And this causes spinlock recursion. Avoid
this by excluding usb_ep_queue from the spinlock.

spin_lock_irqsave //needs cons->lock
gs_console_write
.
.
_printk
__warn_printk
dev_warn/pr_err
.
.
[USB Gadget Layer]
.
.
usb_ep_queue
gs_console_work
__gs_console_push // acquires cons->lock
process_one_work

Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
Link: https://lore.kernel.org/r/1683638872-6885-1-git-send-email-quic_prashk@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

authored by

Prashanth K and committed by
Greg Kroah-Hartman e5990469 2f6ecb89

+3
+3
drivers/usb/gadget/function/u_serial.c
··· 916 916 } 917 917 918 918 req->length = size; 919 + 920 + spin_unlock_irq(&cons->lock); 919 921 if (usb_ep_queue(ep, req, GFP_ATOMIC)) 920 922 req->length = 0; 923 + spin_lock_irq(&cons->lock); 921 924 } 922 925 923 926 static void gs_console_work(struct work_struct *work)