diff mbox series

[v3] serial: stm32: optimize spin lock usage

Message ID 1618567841-18546-1-git-send-email-dillon.minfei@gmail.com (mailing list archive)
State New
Headers show
Series [v3] serial: stm32: optimize spin lock usage | expand

Commit Message

dillon min April 16, 2021, 10:10 a.m. UTC
From: dillon min <dillon.minfei@gmail.com>

This patch aims to fix two potential bug:
- no lock to protect uart register in this case

  stm32_usart_threaded_interrupt()
     spin_lock(&port->lock);
     ...
     stm32_usart_receive_chars()
       uart_handle_sysrq_char();
       sysrq_function();
       printk();
         stm32_usart_console_write();
           locked = 0; //since port->sysrq is not zero,
                         no lock to protect forward register
                         access.

- if add spin_trylock_irqsave() to protect uart register for sysrq = 1 case,
  that might got recursive locking under UP.
  So, use uart_prepare_sysrq_char(), uart_unlock_and_check_sysrq()
  move sysrq handler position to irq/thread_d handler, just record
  sysrq_ch in stm32_usart_receive_chars() by uart_prepare_sysrq_char()
  delay the sysrq process to next interrupt handler.

  new flow:

  stm32_usart_threaded_interrupt()/stm32_usart_interrupt()
  spin_lock_irqsave(&port->lock);
  ...
  uart_unlock_and_check_sysrq();
     spin_unlock_irqrestore();
     handle_sysrq(sysrq_ch);
  stm32_usart_threaded_interrupt()//stm32_usart_interrupt() return

Cc: Johan Hovold <johan@kernel.org>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Gerald Baeza <gerald.baeza@foss.st.com>
Cc: Erwan Le Ray <erwan.leray@foss.st.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: dillon min <dillon.minfei@gmail.com>
---
v3: add uart_prepare_sysrq_char(), uart_unlock_and_check_sysrq() to move
    sysrq handler inside interrupt routinei to avoid recursive locking,
    according to Johan Hovold suggestion, thanks.

 drivers/tty/serial/stm32-usart.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

Comments

Johan Hovold April 16, 2021, 2:10 p.m. UTC | #1
On Fri, Apr 16, 2021 at 06:10:41PM +0800, dillon.minfei@gmail.com wrote:
> From: dillon min <dillon.minfei@gmail.com>
> 
> This patch aims to fix two potential bug:
> - no lock to protect uart register in this case
> 
>   stm32_usart_threaded_interrupt()
>      spin_lock(&port->lock);
>      ...
>      stm32_usart_receive_chars()
>        uart_handle_sysrq_char();
>        sysrq_function();
>        printk();
>          stm32_usart_console_write();
>            locked = 0; //since port->sysrq is not zero,
>                          no lock to protect forward register
>                          access.
> 
> - if add spin_trylock_irqsave() to protect uart register for sysrq = 1 case,
>   that might got recursive locking under UP.
>   So, use uart_prepare_sysrq_char(), uart_unlock_and_check_sysrq()
>   move sysrq handler position to irq/thread_d handler, just record
>   sysrq_ch in stm32_usart_receive_chars() by uart_prepare_sysrq_char()
>   delay the sysrq process to next interrupt handler.
> 
>   new flow:
> 
>   stm32_usart_threaded_interrupt()/stm32_usart_interrupt()
>   spin_lock_irqsave(&port->lock);
>   ...
>   uart_unlock_and_check_sysrq();
>      spin_unlock_irqrestore();
>      handle_sysrq(sysrq_ch);
>   stm32_usart_threaded_interrupt()//stm32_usart_interrupt() return
> 
> Cc: Johan Hovold <johan@kernel.org>
> Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> Cc: Gerald Baeza <gerald.baeza@foss.st.com>
> Cc: Erwan Le Ray <erwan.leray@foss.st.com>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: dillon min <dillon.minfei@gmail.com>
> ---
> v3: add uart_prepare_sysrq_char(), uart_unlock_and_check_sysrq() to move
>     sysrq handler inside interrupt routinei to avoid recursive locking,
>     according to Johan Hovold suggestion, thanks.
> 
>  drivers/tty/serial/stm32-usart.c | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
> index b3675cf25a69..981f50ec784e 100644
> --- a/drivers/tty/serial/stm32-usart.c
> +++ b/drivers/tty/serial/stm32-usart.c
> @@ -271,7 +271,7 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
>  			}
>  		}
>  
> -		if (uart_handle_sysrq_char(port, c))
> +		if (uart_prepare_sysrq_char(port, c))
>  			continue;
>  		uart_insert_char(port, sr, USART_SR_ORE, c, flag);
>  	}
> @@ -457,9 +457,10 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
>  	struct uart_port *port = ptr;
>  	struct stm32_port *stm32_port = to_stm32_port(port);
>  	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
> +	unsigned long flags;
>  	u32 sr;
>  
> -	spin_lock(&port->lock);
> +	spin_lock_irqsave(&port->lock, flags);
>  
>  	sr = readl_relaxed(port->membase + ofs->isr);
>  
> @@ -477,7 +478,7 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
>  	if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch))
>  		stm32_usart_transmit_chars(port);
>  
> -	spin_unlock(&port->lock);
> +	uart_unlock_and_check_sysrq(port, flags);
>  
>  	if (stm32_port->rx_ch)
>  		return IRQ_WAKE_THREAD;
> @@ -489,13 +490,14 @@ static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
>  {
>  	struct uart_port *port = ptr;
>  	struct stm32_port *stm32_port = to_stm32_port(port);
> +	unsigned long flags;
>  
> -	spin_lock(&port->lock);
> +	spin_lock_irqsave(&port->lock, flags);

This essentially turns the threaded handler into a non-threaded one,
which is a bad idea.

>  	if (stm32_port->rx_ch)
>  		stm32_usart_receive_chars(port, true);
>  
> -	spin_unlock(&port->lock);
> +	uart_unlock_and_check_sysrq(port, flags);
>  
>  	return IRQ_HANDLED;
>  }

You also didn't base this patch on tty-next, which has a number of
updates to this driver. Before noting that myself, I had fixed a couple
of deadlocks in this driver which turned out to have been incidentally
fixed by an unrelated path in -next.

I'll be posting a series that should fix up all of this.

Johan
dillon min April 17, 2021, 1:07 p.m. UTC | #2
Hi Johan,

On Fri, Apr 16, 2021 at 10:10 PM Johan Hovold <johan@kernel.org> wrote:
>
> On Fri, Apr 16, 2021 at 06:10:41PM +0800, dillon.minfei@gmail.com wrote:
> > From: dillon min <dillon.minfei@gmail.com>
> >
> > This patch aims to fix two potential bug:
> > - no lock to protect uart register in this case
> >
> >   stm32_usart_threaded_interrupt()
> >      spin_lock(&port->lock);
> >      ...
> >      stm32_usart_receive_chars()
> >        uart_handle_sysrq_char();
> >        sysrq_function();
> >        printk();
> >          stm32_usart_console_write();
> >            locked = 0; //since port->sysrq is not zero,
> >                          no lock to protect forward register
> >                          access.
> >
> > - if add spin_trylock_irqsave() to protect uart register for sysrq = 1 case,
> >   that might got recursive locking under UP.
> >   So, use uart_prepare_sysrq_char(), uart_unlock_and_check_sysrq()
> >   move sysrq handler position to irq/thread_d handler, just record
> >   sysrq_ch in stm32_usart_receive_chars() by uart_prepare_sysrq_char()
> >   delay the sysrq process to next interrupt handler.
> >
> >   new flow:
> >
> >   stm32_usart_threaded_interrupt()/stm32_usart_interrupt()
> >   spin_lock_irqsave(&port->lock);
> >   ...
> >   uart_unlock_and_check_sysrq();
> >      spin_unlock_irqrestore();
> >      handle_sysrq(sysrq_ch);
> >   stm32_usart_threaded_interrupt()//stm32_usart_interrupt() return
> >
> > Cc: Johan Hovold <johan@kernel.org>
> > Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
> > Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> > Cc: Gerald Baeza <gerald.baeza@foss.st.com>
> > Cc: Erwan Le Ray <erwan.leray@foss.st.com>
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: dillon min <dillon.minfei@gmail.com>
> > ---
> > v3: add uart_prepare_sysrq_char(), uart_unlock_and_check_sysrq() to move
> >     sysrq handler inside interrupt routinei to avoid recursive locking,
> >     according to Johan Hovold suggestion, thanks.
> >
> >  drivers/tty/serial/stm32-usart.c | 24 +++++++++++-------------
> >  1 file changed, 11 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
> > index b3675cf25a69..981f50ec784e 100644
> > --- a/drivers/tty/serial/stm32-usart.c
> > +++ b/drivers/tty/serial/stm32-usart.c
> > @@ -271,7 +271,7 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
> >                       }
> >               }
> >
> > -             if (uart_handle_sysrq_char(port, c))
> > +             if (uart_prepare_sysrq_char(port, c))
> >                       continue;
> >               uart_insert_char(port, sr, USART_SR_ORE, c, flag);
> >       }
> > @@ -457,9 +457,10 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
> >       struct uart_port *port = ptr;
> >       struct stm32_port *stm32_port = to_stm32_port(port);
> >       const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
> > +     unsigned long flags;
> >       u32 sr;
> >
> > -     spin_lock(&port->lock);
> > +     spin_lock_irqsave(&port->lock, flags);
> >
> >       sr = readl_relaxed(port->membase + ofs->isr);
> >
> > @@ -477,7 +478,7 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
> >       if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch))
> >               stm32_usart_transmit_chars(port);
> >
> > -     spin_unlock(&port->lock);
> > +     uart_unlock_and_check_sysrq(port, flags);
> >
> >       if (stm32_port->rx_ch)
> >               return IRQ_WAKE_THREAD;
> > @@ -489,13 +490,14 @@ static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
> >  {
> >       struct uart_port *port = ptr;
> >       struct stm32_port *stm32_port = to_stm32_port(port);
> > +     unsigned long flags;
> >
> > -     spin_lock(&port->lock);
> > +     spin_lock_irqsave(&port->lock, flags);
>
> This essentially turns the threaded handler into a non-threaded one,
> which is a bad idea.
This change is only to adapt for uart_unlock_and_check_sysrq() need flags.
Found your patch has removed this parameter from
uart_unlock_and_check_sysrq(), so this changes should be removed.

>
> >       if (stm32_port->rx_ch)
> >               stm32_usart_receive_chars(port, true);
> >
> > -     spin_unlock(&port->lock);
> > +     uart_unlock_and_check_sysrq(port, flags);
> >
> >       return IRQ_HANDLED;
> >  }
>
> You also didn't base this patch on tty-next, which has a number of
> updates to this driver. Before noting that myself, I had fixed a couple
> of deadlocks in this driver which turned out to have been incidentally
> fixed by an unrelated path in -next.
Yes, my submission is based on linux-5.12. based on the component's
next branch is a good idea , to avoid conflict. thanks.
>
> I'll be posting a series that should fix up all of this.
Thanks
>
> Johan
diff mbox series

Patch

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index b3675cf25a69..981f50ec784e 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -271,7 +271,7 @@  static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
 			}
 		}
 
-		if (uart_handle_sysrq_char(port, c))
+		if (uart_prepare_sysrq_char(port, c))
 			continue;
 		uart_insert_char(port, sr, USART_SR_ORE, c, flag);
 	}
@@ -457,9 +457,10 @@  static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 	struct uart_port *port = ptr;
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+	unsigned long flags;
 	u32 sr;
 
-	spin_lock(&port->lock);
+	spin_lock_irqsave(&port->lock, flags);
 
 	sr = readl_relaxed(port->membase + ofs->isr);
 
@@ -477,7 +478,7 @@  static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
 	if ((sr & USART_SR_TXE) && !(stm32_port->tx_ch))
 		stm32_usart_transmit_chars(port);
 
-	spin_unlock(&port->lock);
+	uart_unlock_and_check_sysrq(port, flags);
 
 	if (stm32_port->rx_ch)
 		return IRQ_WAKE_THREAD;
@@ -489,13 +490,14 @@  static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
 {
 	struct uart_port *port = ptr;
 	struct stm32_port *stm32_port = to_stm32_port(port);
+	unsigned long flags;
 
-	spin_lock(&port->lock);
+	spin_lock_irqsave(&port->lock, flags);
 
 	if (stm32_port->rx_ch)
 		stm32_usart_receive_chars(port, true);
 
-	spin_unlock(&port->lock);
+	uart_unlock_and_check_sysrq(port, flags);
 
 	return IRQ_HANDLED;
 }
@@ -1354,13 +1356,10 @@  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);
+	if (oops_in_progress)
+		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)