On Mon, Aug 10, 2015 at 12:15:40AM +0000, Taichi Kageyama wrote: > The following race conditions can happen when a serial port is used > as console. > > Case1: CPU_B is used to detect an interrupt from a serial port, > but it can have interrupts disabled during the waiting time. > Case2: CPU_B clears UART_IER just after CPU_A sets UART_IER and then > a serial port may not make an interrupt. > Case3: CPU_A sets UART_IER just after CPU_B clears UART_IER. > This is an unexpected behavior for serial8250_console_write(). > > CPU_A [autoconfig_irq] | CPU_B [serial8250_console_write] > ----------------------------|--------------------------------------- > | > probe_irq_on() | spin_lock_irqsave(&port->lock,) > serial_outp(,UART_IER,0x0f) | serial_out(,UART_IER,0) > udelay(20); | uart_console_write() > probe_irq_off() | > | spin_unlock_irqrestore(&port->lock,) > > Case1 and 2 can make autoconfig_irq() failed. > In these cases, the console doesn't work in interrupt mode and > "input overrun" (which can make operation mistakes) can happen > on some systems. Especially in the Case1, It is known that the > problem happens with high rate every boot once it occurs > because the boot sequence is always almost same. > > port mutex makes sure that the autoconfig operation is exclusive of > any other concurrent HW access except by the console operation. > console lock is required in autoconfig_irq(). > > Signed-off-by: Taichi Kageyama <t-kageyama@xxxxxxxxxxxxx> > Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > Reviewed-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> > --- > drivers/tty/serial/8250/8250_core.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git v4.2-rc4.org/drivers/tty/serial/8250/8250_core.c v4.2-rc4.work/drivers/tty/serial/8250/8250_core.c > index 37fff12..ed1e23e 100644 > --- v4.2-rc4.org/drivers/tty/serial/8250/8250_core.c > +++ v4.2-rc4.work/drivers/tty/serial/8250/8250_core.c > @@ -1303,6 +1303,9 @@ static void autoconfig_irq(struct uart_8250_port *up) > inb_p(ICP); > } > > + if (uart_console(port)) > + console_lock(); > + > /* forget possible initially masked and pending IRQ */ > probe_irq_off(probe_irq_on()); > save_mcr = serial_in(up, UART_MCR); > @@ -1334,6 +1337,9 @@ static void autoconfig_irq(struct uart_8250_port *up) > if (port->flags & UPF_FOURPORT) > outb_p(save_ICP, ICP); > > + if (uart_console(port)) > + console_unlock(); > + > port->irq = (irq > 0) ? irq : 0; > } This doesn't apply to my tty-next tree at all. Can you please rebase it and resend? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
