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

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

Jürgen Groß <jgross@xxxxxxxx> writes:

> 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?

Darn. Of course does this need to be there. Stupid me, let me resend.

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