Hi Greg, On 2015/08/15 9:10, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > 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? Oh, I didn't know the file name was changed in tty-next. I'll rebase it. Thanks, Taichi -- 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
