linux-kernel - [PATCH 8/8] x86/entry, bug: Comment the instrumentation

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Date:   Thu, 04 Jun 2020 12:22:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     tglx@...utronix.de
Cc:     x86@...nel.org, elver@...gle.com, paulmck@...nel.org,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        peterz@...radead.org, will@...nel.org, dvyukov@...gle.com,
        glider@...gle.com, andreyknvl@...gle.com
Subject: [PATCH 8/8] x86/entry, bug: Comment the instrumentation_begin() usage for WARN()

Explain the rationale for annotating WARN(), even though, strictly
speaking printk() and friends are very much not safe in many of the
places we put them.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/bug.h |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -76,6 +76,12 @@ do {								\
 	unreachable();						\
 } while (0)
 
+/*
+ * This instrumentation_begin() is strictly speaking incorrect; but it
+ * suppresses the complaints from WARN()s in noinstr code. If such a WARN()
+ * were to trigger, we'd rather wreck the machine in an attempt to get the
+ * message out than not know about it.
+ */
 #define __WARN_FLAGS(flags)					\
 do {								\
 	instrumentation_begin();				\