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SubjectRe: [PATCH 1/2] serial: 8250: Fix autoconfig_irq() to avoid race conditions
On Fri, Jun 05, 2015 at 09:57:40AM +0000, Taichi Kageyama wrote:
> The following race conditions can happen if a serial is used as console.
> Case1. CPU_B handles an interrupt from a serial
> autoconfig_irq() fails whether the interrupt is raised or not
> if CPU_B is disabled to handle interrupts for longer than it expects.
> Case2. CPU_B clears UART_IER just after CPU_A sets UART_IER
> A serial may not make an interrupt.
> autoconfig_irq() can fail if the interrupt is not raised.
> Case3. CPU_A sets UART_IER just after CPU_B clears UART_IER
> This is an unexpected behavior for uart_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,)
> -----------------------------------------------------------------
>
> If autoconfig_irq() fails, the console doesn't work in interrupt mode,
> the mode cannot be changed anymore, and "input overrun"
> (which can make operation mistakes) happens easily.
> This problem happens with high rate every boot once it occurs
> because the boot sequence is always almost same.
>
> Signed-off-by: Taichi Kageyama <t-kageyama@cp.jp.nec.com>
> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
> ---
> drivers/tty/serial/8250/8250_core.c | 6 ++++++
> 1 files changed, 6 insertions(+), 0 deletions(-)

Does not apply to 4.2-rc3 :(


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