From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> Sent: Thursday, November 12, 2020 4:40 PM
> On Wed, Nov 11, 2020 at 10:51:36AM +0800, Fugang Duan wrote:
> > For below code, there has chance to cause deadlock in SMP system:
> > Thread 1:
> > clk_enable_lock();
> > pr_info("debug message");
> > clk_enable_unlock();
> >
> > Thread 2:
> > imx_uart_console_write()
> > clk_enable()
> > clk_enable_lock();
> >
> > Thread 1:
> > Acuired clk enable_lock -> printk -> console_trylock_spinning Thread
> > 2:
> > console_unlock() -> imx_uart_console_write -> clk_disable -> Acquite
> > clk enable_lock
> >
> > So the patch is to keep console port clocks always on like other
> > console drivers.
> >
> > Fixes: 1cf93e0d5488 ("serial: imx: remove the uart_console() check")
> > Signed-off-by: Fugang Duan <fugang.duan@xxxxxxx>
> > ---
> > v2: Add fixes tag in commit message.
> > ---
> > drivers/tty/serial/imx.c | 19 +++----------------
> > 1 file changed, 3 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c index
> > 1731d9728865..4d6c009ddc31 100644
> > --- a/drivers/tty/serial/imx.c
> > +++ b/drivers/tty/serial/imx.c
> > @@ -2004,15 +2004,6 @@ imx_uart_console_write(struct console *co, const
> char *s, unsigned int count)
> > int locked = 1;
> > int retval;
> >
> > - retval = clk_enable(sport->clk_per);
> > - if (retval)
> > - return;
> > - retval = clk_enable(sport->clk_ipg);
> > - if (retval) {
> > - clk_disable(sport->clk_per);
> > - return;
> > - }
> > -
> > if (sport->port.sysrq)
> > locked = 0;
> > else if (oops_in_progress)
> > @@ -2047,9 +2038,6 @@ imx_uart_console_write(struct console *co, const
> > char *s, unsigned int count)
> >
> > if (locked)
> > spin_unlock_irqrestore(&sport->port.lock, flags);
> > -
> > - clk_disable(sport->clk_ipg);
> > - clk_disable(sport->clk_per);
> > }
> >
> > /*
> > @@ -2150,15 +2138,14 @@ imx_uart_console_setup(struct console *co,
> > char *options)
> >
> > retval = uart_set_options(&sport->port, co, baud, parity, bits,
> > flow);
> >
> > - clk_disable(sport->clk_ipg);
> > if (retval) {
> > - clk_unprepare(sport->clk_ipg);
> > + clk_disable_unprepare(sport->clk_ipg);
> > goto error_console;
> > }
> >
> > - retval = clk_prepare(sport->clk_per);
> > + retval = clk_prepare_enable(sport->clk_per);
> > if (retval)
> > - clk_unprepare(sport->clk_ipg);
> > + clk_disable_unprepare(sport->clk_ipg);
> >
> > error_console:
> > return retval;
> > --
> > 2.17.1
> >
>
> Did you test build this change and totally ignore the build warning you now get:
>
> drivers/tty/serial/imx.c: In function ‘imx_uart_console_write’:
> drivers/tty/serial/imx.c:2011:6: warning: unused variable ‘retval’
> [-Wunused-variable]
> 2011 | int retval;
> | ^~~~~~
>
> Not good...
>
> I'll go fix it.
>
> greg k-h
Thanks, Greg, I ignore the build warning.
Andy
