Re: [PATCH] xen: Enable interrupts when calling _cond_resched()

[JÃrgen GroÃ]

On 19.02.20 12:01, Thomas Gleixner wrote:
> xen_maybe_preempt_hcall() is called from the exception entry point
> xen_do_hypervisor_callback with interrupts disabled.
>
> _cond_resched() evades the might_sleep() check in cond_resched() which
> would have caught that and schedule_debug() unfortunately lacks a check
> for irqs_disabled().
>
> Enable interrupts around the call and use cond_resched() to catch future
> issues.
>
> Fixes: fdfd811ddde3 ("x86/xen: allow privcmd hypercalls to be preempted")
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>   drivers/xen/preempt.c |    4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> --- a/drivers/xen/preempt.c
> +++ b/drivers/xen/preempt.c
> @@ -33,8 +33,10 @@ asmlinkage __visible void xen_maybe_pree
>   		 * cpu.
>   		 */
>   		__this_cpu_write(xen_in_preemptible_hcall, false);
> -		_cond_resched();
> +		local_irq_enable();
> +		cond_resched();
>   		__this_cpu_write(xen_in_preemptible_hcall, true);
> +		local_irq_disable();

Could you please put the call of local_irq_disable() directly after the
cond_resched() call to make the result symmetric regarding writing of
xen_in_preemptible_hcall and irq enable/disable?


Juergen