linux-kernel - [PATCH v4 02/10] include/linux/compiler.h: Introduce data

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Message-Id: <20191114180303.66955-3-elver@google.com>
Date:   Thu, 14 Nov 2019 19:02:55 +0100
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com
Cc:     akiyks@...il.com, stern@...land.harvard.edu, glider@...gle.com,
        parri.andrea@...il.com, andreyknvl@...gle.com, luto@...nel.org,
        ard.biesheuvel@...aro.org, arnd@...db.de, boqun.feng@...il.com,
        bp@...en8.de, dja@...ens.net, dlustig@...dia.com,
        dave.hansen@...ux.intel.com, dhowells@...hat.com,
        dvyukov@...gle.com, hpa@...or.com, mingo@...hat.com,
        j.alglave@....ac.uk, joel@...lfernandes.org, corbet@....net,
        jpoimboe@...hat.com, luc.maranget@...ia.fr, mark.rutland@....com,
        npiggin@...il.com, paulmck@...nel.org, peterz@...radead.org,
        tglx@...utronix.de, will@...nel.org, edumazet@...gle.com,
        kasan-dev@...glegroups.com, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH v4 02/10] include/linux/compiler.h: Introduce data_race(expr) macro

This introduces the data_race(expr) macro, which can be used to annotate
expressions for purposes of (1) documenting, and (2) giving tooling such
as KCSAN information about which data races are deemed "safe".

More context:
http://lkml.kernel.org/r/CAHk-=wg5CkOEF8DTez1Qu0XTEFw_oHhxN98bDnFqbY7HL5AB2g@mail.gmail.com

Signed-off-by: Marco Elver <elver@...gle.com>
Cc: Alan Stern <stern@...land.harvard.edu>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E. McKenney <paulmck@...nel.org>
---
v4:
* Introduce this patch to KCSAN series.
---
 include/linux/compiler.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index c42fa83f23fb..7d3e77781578 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -310,6 +310,26 @@ unsigned long read_word_at_a_time(const void *addr)
 	__u.__val;					\
 })
 
+#include <linux/kcsan.h>
+
+/*
+ * data_race: macro to document that accesses in an expression may conflict with
+ * other concurrent accesses resulting in data races, but the resulting
+ * behaviour is deemed safe regardless.
+ *
+ * This macro *does not* affect normal code generation, but is a hint to tooling
+ * that data races here should be ignored.
+ */
+#define data_race(expr)                                                        \
+	({                                                                     \
+		typeof(({ expr; })) __val;                                     \
+		kcsan_nestable_atomic_begin();                                 \
+		__val = ({ expr; });                                           \
+		kcsan_nestable_atomic_end();                                   \
+		__val;                                                         \
+	})
+#else
+
 #endif /* __KERNEL__ */
 
 /*
-- 
2.24.0.rc1.363.gb1bccd3e3d-goog