[PATCH 3.14 64/98] USB: console: fix uninitialised ldisc semaphore

Greg Kroah-Hartman
2015-01-25T19:09:38Z

From: Johan Hovold <johan@kernel.org>

commit d269d4434c72ed0da3a9b1230c30da82c4918c63 upstream.

The USB console currently allocates a temporary fake tty which is used
to pass terminal settings to the underlying serial driver.

The tty struct is not fully initialised, something which can lead to a
lockdep warning (or worse) if a serial driver tries to acquire a
line-discipline reference:

usbserial: USB Serial support registered for pl2303
pl2303 1-2.1:1.0: pl2303 converter detected
usb 1-2.1: pl2303 converter now attached to ttyUSB0
INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
CPU: 0 PID: 68 Comm: udevd Tainted: G W 3.18.0-rc5 #10
[<c0016f04>] (unwind_backtrace) from [<c0013978>] (show_stack+0x20/0x24)
[<c0013978>] (show_stack) from [<c0449794>] (dump_stack+0x24/0x28)
[<c0449794>] (dump_stack) from [<c006f730>] (__lock_acquire+0x1e50/0x2004)
[<c006f730>] (__lock_acquire) from [<c0070128>] (lock_acquire+0xe4/0x18c)
[<c0070128>] (lock_acquire) from [<c027c6f8>] (ldsem_down_read_trylock+0x78/0x90)
[<c027c6f8>] (ldsem_down_read_trylock) from [<c027a1cc>] (tty_ldisc_ref+0x24/0x58)
[<c027a1cc>] (tty_ldisc_ref) from [<c0340760>] (usb_serial_handle_dcd_change+0x48/0xe8)
[<c0340760>] (usb_serial_handle_dcd_change) from [<bf000484>] (pl2303_read_int_callback+0x210/0x220 [pl2303])
[<bf000484>] (pl2303_read_int_callback [pl2303]) from [<c031624c>] (__usb_hcd_giveback_urb+0x80/0x140)
[<c031624c>] (__usb_hcd_giveback_urb) from [<c0316fc0>] (usb_giveback_urb_bh+0x98/0xd4)
[<c0316fc0>] (usb_giveback_urb_bh) from [<c0042e44>] (tasklet_hi_action+0x9c/0x108)
[<c0042e44>] (tasklet_hi_action) from [<c0042380>] (__do_softirq+0x148/0x42c)
[<c0042380>] (__do_softirq) from [<c00429cc>] (irq_exit+0xd8/0x114)
[<c00429cc>] (irq_exit) from [<c007ae58>] (__handle_domain_irq+0x84/0xdc)
[<c007ae58>] (__handle_domain_irq) from [<c000879c>] (omap_intc_handle_irq+0xd8/0xe0)
[<c000879c>] (omap_intc_handle_irq) from [<c0014544>] (__irq_svc+0x44/0x7c)
Exception stack(0xdf4e7f08 to 0xdf4e7f50)
7f00: debc0b80 df4e7f5c 00000000 00000000 debc0b80 be8da96c
7f20: 00000000 00000128 c000fc84 df4e6000 00000000 df4e7f94 00000004 df4e7f50
7f40: c038ebc0 c038d74c 600f0013 ffffffff
[<c0014544>] (__irq_svc) from [<c038d74c>] (___sys_sendmsg.part.29+0x0/0x2e0)
[<c038d74c>] (___sys_sendmsg.part.29) from [<c038ec08>] (SyS_sendmsg+0x18/0x1c)
[<c038ec08>] (SyS_sendmsg) from [<c000fa00>] (ret_fast_syscall+0x0/0x48)
console [ttyUSB0] enabled

Fixes: 36697529b5bb ("tty: Replace ldisc locking with ldisc_sem")
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/serial/console.c | 1 +
1 file changed, 1 insertion(+)

--- a/drivers/usb/serial/console.c
+++ b/drivers/usb/serial/console.c
@@ -140,6 +140,7 @@ static int usb_console_setup(struct cons
tty_port_tty_set(&port->port, tty);
tty->driver = usb_serial_tty_driver;
tty->index = co->index;
+ init_ldsem(&tty->ldisc_sem);
if (tty_init_termios(tty)) {
retval = -ENOMEM;
goto free_tty;