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

From: JÃrgen GroÃ
Date: Wed Feb 19 2020 - 07:03:02 EST

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

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?