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

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Date:   Mon, 15 Jun 2020 22:31:42 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/entry] x86/entry, bug: Comment the instrumentation_begin()
 usage for WARN()

The following commit has been merged into the x86/entry branch of tip:

Commit-ID:     8e8bb06d199a5aa7a534aa3b3fc0abbbc11ca438
Gitweb:        https://git.kernel.org/tip/8e8bb06d199a5aa7a534aa3b3fc0abbbc11ca438
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 04 Jun 2020 11:17:40 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 15 Jun 2020 14:10:10 +02:00

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(+)

diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index fb34ff6..0281895 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -75,6 +75,12 @@ 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();				\