On Mon, Apr 12, 2021 at 05:31:38PM +0800, dillon.minfei(a)gmail.com wrote: 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? Johan

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(a)gmail.com&gt; 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(a)kernel.org&gt; wrote: > > > > On Mon, Apr 12, 2021 at 05:31:38PM +0800, dillon.minfei(a)gmail.com wrote: > > > From: dillon min <dillon.minfei(a)gmail.com&gt; > > > > > > 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(a)foss.st.com&gt; > > > Cc: Maxime Coquelin <mcoquelin.stm32(a)gmail.com&gt; > > > Cc: Gerald Baeza <gerald.baeza(a)foss.st.com&gt; > > > Cc: Erwan Le Ray <erwan.leray(a)foss.st.com&gt; > > > Reported-by: kernel test robot <lkp(a)intel.com&gt; > > > Signed-off-by: dillon min <dillon.minfei(a)gmail.com&gt; > > > --- > > > 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

Hi Erwan, Erwan LE RAY <erwan.leray(a)foss.st.com&gt; 于2021年4月16日周五 上午1:10写道： Thanks. Thanks for the detail information. the V2 patch didn't cover this case: stm32_usart_threaded_interrupt() spin_lock(&port->lock); ... uart_handle_sysrq_char(); sysrq_function(); printk(); stm32_usart_console_write(); locked = spin_trylock_irqsave(&port->lock); //better than no lock(locked = 0) if other uart interrupt coming at this point Find a same solution on fsl_lpuart.c commit abf1e0a98083fd0a1069ce68ad8c92bfb97a57db Thanks. Best regards Dillon > > So your initial patch looks to the right proposal, but it would be safer > if Greg could confirm it. > > BR, Erwan. > > > On 4/13/21 1:44 AM, dillon min wrote: > > 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(a)gmail.com&gt; 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(a)kernel.org&gt; wrote: > >>> > >>> On Mon, Apr 12, 2021 at 05:31:38PM +0800, dillon.minfei(a)gmail.com wrote: > >>>> From: dillon min <dillon.minfei(a)gmail.com&gt; > >>>> > >>>> 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(a)foss.st.com&gt; > >>>> Cc: Maxime Coquelin <mcoquelin.stm32(a)gmail.com&gt; > >>>> Cc: Gerald Baeza <gerald.baeza(a)foss.st.com&gt; > >>>> Cc: Erwan Le Ray <erwan.leray(a)foss.st.com&gt; > >>>> Reported-by: kernel test robot <lkp(a)intel.com&gt; > >>>> Signed-off-by: dillon min <dillon.minfei(a)gmail.com&gt; > >>>> --- > >>>> 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