linux-kernel - [PATCH RT 04/23] x86: preempt: Check preemption level before looking at lazy-preempt

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Date:   Thu, 27 Feb 2020 08:33:15 -0600
From:   zanussi@...nel.org
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>
Subject: [PATCH RT 04/23] x86: preempt: Check preemption level before looking at lazy-preempt

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

v4.14.170-rt75-rc2 stable review patch.
If anyone has any objections, please let me know.

-----------


[ Upstream commit 19fc8557f2323c52b26561651ed4d51fc688a740 ]

Before evaluating the lazy-preempt state it must be ensure that the
preempt-count is zero.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Tom Zanussi <zanussi@...nel.org>
---
 arch/x86/include/asm/preempt.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index f66708779274..afa0e42ccdd1 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -96,6 +96,8 @@ static __always_inline bool __preempt_count_dec_and_test(void)
 	if (____preempt_count_dec_and_test())
 		return true;
 #ifdef CONFIG_PREEMPT_LAZY
+	if (preempt_count())
+		return false;
 	if (current_thread_info()->preempt_lazy_count)
 		return false;
 	return test_thread_flag(TIF_NEED_RESCHED_LAZY);
-- 
2.14.1