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