linux-kernel - [PATCH] xen: Enable interrupts when calling _cond

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Message-ID: <87tv3mq1rm.fsf@nanos.tec.linutronix.de>
Date:   Wed, 19 Feb 2020 12:01:33 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org
Subject: [PATCH] xen: Enable interrupts when calling _cond_resched()

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@...utronix.de>
---
 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();
 	}
 }
 #endif /* CONFIG_PREEMPTION */