[kbuild-all] Re: [PATCH v3] serial: stm32: optimize spin lock usage

On Fri, Apr 16, 2021 at 06:10:41PM +0800, dillon.minfei(a)gmail.com wrote: > From: dillon min <dillon.minfei(a)gmail.com&gt; > > 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(a)kernel.org&gt; > 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; > --- > 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.