linux-kernel - [PATCH RT 2/2] x86: lazy-preempt: properly check against preempt-mask

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Date:   Mon, 18 Feb 2019 17:31:37 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-rt-users@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH RT 2/2] x86: lazy-preempt: properly check against preempt-mask

should_resched() should check against preempt_offset after unmasking the
need-resched-bit. Otherwise should_resched() won't work for
preempt_offset != 0 and lazy-preempt set.

Cc: stable-rt@...r.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 arch/x86/include/asm/preempt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 22992c8377952..f667087792747 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -118,7 +118,7 @@ static __always_inline bool should_resched(int preempt_offset)
 
 	/* preempt count == 0 ? */
 	tmp &= ~PREEMPT_NEED_RESCHED;
-	if (tmp)
+	if (tmp != preempt_offset)
 		return false;
 	if (current_thread_info()->preempt_lazy_count)
 		return false;
-- 
2.20.1