Re: [patch part-II V2 13/13] x86/entry/common: Split irq tracing in prepare_exit_to_usermode()

Alexandre Chartre
2020-03-10T14:10:31Z

On 3/8/20 11:24 PM, Thomas Gleixner wrote:
> As in entry from user mode, lockdep and tracing have different
> requirements. lockdep needs to know about the interrupts off state accross
> the call to user_enter_irqsoff() but tracing is unsafe after the call.

typo: user_enter_irqoff() (no 's' between 'irq' and 'off').

>
> Split it up and tell the tracer that interrupts are going to be enabled
> before calling user_enter_irqsoff() and tell lockdep afterwards.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/entry/common.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -251,9 +251,19 @@ static noinline void __prepare_exit_to_u
> {
> __prepare_exit_to_usermode(regs);
>
> + /*
> + * Return to user space enables interrupts. Tell the tracer before
> + * invoking user_enter_irqsoff() which switches to CONTEXT_USER and

Same typo here: user_enter_irqoff()

> + * RCU to rcuidle state. Lockdep still needs to keep the irqs
> + * disabled state.
> + */
> + __trace_hardirqs_on();
> +
> user_enter_irqoff();
> mds_user_clear_cpu_buffers();
> - trace_hardirqs_on();
> +
> + /* All done. Tell lockdep as well. */
> + lockdep_hardirqs_on(CALLER_ADDR0);
> }
> NOKPROBE_SYMBOL(prepare_exit_to_usermode);
>
>

Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

alex.