Hi Johan, Erwan
It seems still a bit of a problem in the current version, not deadlock
but access register at the same time.
For driver , we should consider it running under smp, let's think
about it for this case:
static void stm32_usart_console_write(struct console *co, const char *s,
unsigned int cnt)
{
.....
local_irq_save(flags);
if (port->sysrq)
locked = 0;
.....
access register cr1, tdr, isr
.....
local_irq_restore(flags);
}
if port->sysrq is 1, stm32_usart_console_write() just disable local
irq response by local_irq_save(), at the time of access register cr1,
tdr, isr. an TXE interrupt raised, for other cores(I know stm32
mpu/mcu do not have multi cores, just assume it has), it still has a
chance to handle interrupt. Then there is no lock to protect the uart
register.
changes to below, should be more safe:
.....
if (port->sysrq || oops_in_progress)
locked = spin_trylock_irqsave(&port->lock, flags);
else
spin_lock_irqsave(&port->lock, flags);
....
if (locked)
spin_unlock_irqrestore(&port->lock, flags);
For current stm32 soc, it shouldn't happen. just a reminder for future.
Thanks.
Dillon
On Mon, Apr 12, 2021 at 10:04 PM dillon min <dillon.minfei@xxxxxxxxx> wrote:
>
> Hi Johan,
>
> Yes, there is no deadlock. my fault.
> I forget the local_irq_save() plus spin_lock() is spin_lock_irqsave().
>
> Thanks for your review. please ignore this patch.
>
> Best regards
>
> Dillon
>
> On Mon, Apr 12, 2021 at 9:08 PM Johan Hovold <johan@xxxxxxxxxx> wrote:
> >
> > On Mon, Apr 12, 2021 at 05:31:38PM +0800, dillon.minfei@xxxxxxxxx wrote:
> > > From: dillon min <dillon.minfei@xxxxxxxxx>
> > >
> > > To avoid potential deadlock in spin_lock usage, use spin_lock_irqsave,
> > > spin_trylock_irqsave(), spin_unlock_irqrestore() in process context.
> >
> > This doesn't make much sense as console_write can be called in any
> > context. And where's the deadlock you claim to be fixing here?
> >
> > > remove unused local_irq_save/restore call.
> > >
> > > Cc: Alexandre Torgue <alexandre.torgue@xxxxxxxxxxx>
> > > Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
> > > Cc: Gerald Baeza <gerald.baeza@xxxxxxxxxxx>
> > > Cc: Erwan Le Ray <erwan.leray@xxxxxxxxxxx>
> > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > Signed-off-by: dillon min <dillon.minfei@xxxxxxxxx>
> > > ---
> > > v2: remove unused code from stm32_usart_threaded_interrupt() according from
> > > Greg's review.
> > >
> > > drivers/tty/serial/stm32-usart.c | 8 +++-----
> > > 1 file changed, 3 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
> > > index b3675cf25a69..b1ba5e36e36e 100644
> > > --- a/drivers/tty/serial/stm32-usart.c
> > > +++ b/drivers/tty/serial/stm32-usart.c
> > > @@ -1354,13 +1354,12 @@ static void stm32_usart_console_write(struct console *co, const char *s,
> > > u32 old_cr1, new_cr1;
> > > int locked = 1;
> > >
> > > - local_irq_save(flags);
> > > if (port->sysrq)
> > > locked = 0;
> > > else if (oops_in_progress)
> > > - locked = spin_trylock(&port->lock);
> > > + locked = spin_trylock_irqsave(&port->lock, flags);
> > > else
> > > - spin_lock(&port->lock);
> > > + spin_lock_irqsave(&port->lock, flags);
> > >
> > > /* Save and disable interrupts, enable the transmitter */
> > > old_cr1 = readl_relaxed(port->membase + ofs->cr1);
> > > @@ -1374,8 +1373,7 @@ static void stm32_usart_console_write(struct console *co, const char *s,
> > > writel_relaxed(old_cr1, port->membase + ofs->cr1);
> > >
> > > if (locked)
> > > - spin_unlock(&port->lock);
> > > - local_irq_restore(flags);
> > > + spin_unlock_irqrestore(&port->lock, flags);
> > > }
> > >
> > > static int stm32_usart_console_setup(struct console *co, char *options)
> >
> > Johan
