Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 08 May 2020 13:46:33 -0000
From:   "tip-bot2 for Marco Elver" <tip-bot2@linutronix.de>
Reply-to: linux-kernel@vger.kernel.org
To:     linux-tip-commits@vger.kernel.org
Subject: [tip: locking/kcsan] kcsan: Change data_race() to no longer require
 marking racing accesses
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Will Deacon <will@kernel.org>, Qian Cai <cai@lca.pw>,
        Marco Elver <elver@google.com>, x86 <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
In-Reply-To: <20200331131002.GA30975@willie-the-truck>
References: <20200331131002.GA30975@willie-the-truck>
MIME-Version: 1.0
Message-ID: <158894559307.8414.14354210811122295104.tip-bot2@tip-bot2>
Robot-ID: <tip-bot2.linutronix.de>
Robot-Unsubscribe: Contact <mailto:tglx@linutronix.de> to get blacklisted from these emails
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The following commit has been merged into the locking/kcsan branch of tip:

Commit-ID:     d071e91361bbfef524ae8abf7e560fb294d0ad64
Gitweb:        https://git.kernel.org/tip/d071e91361bbfef524ae8abf7e560fb294d0ad64
Author:        Marco Elver <elver@google.com>
AuthorDate:    Tue, 31 Mar 2020 21:32:33 +02:00
Committer:     Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Mon, 13 Apr 2020 17:18:15 -07:00

kcsan: Change data_race() to no longer require marking racing accesses

Thus far, accesses marked with data_race() would still require the
racing access to be marked in some way (be it with READ_ONCE(),
WRITE_ONCE(), or data_race() itself), as otherwise KCSAN would still
report a data race.  This requirement, however, seems to be unintuitive,
and some valid use-cases demand *not* marking other accesses, as it
might hide more serious bugs (e.g. diagnostic reads).

Therefore, this commit changes data_race() to no longer require marking
racing accesses (although it's still recommended if possible).

The alternative would have been introducing another variant of
data_race(), however, since usage of data_race() already needs to be
carefully reasoned about, distinguishing between these cases likely adds
more complexity in the wrong place.

Link: https://lkml.kernel.org/r/20200331131002.GA30975@willie-the-truck
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Qian Cai <cai@lca.pw>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 include/linux/compiler.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index f504ede..1729bd1 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -326,9 +326,9 @@ unsigned long read_word_at_a_time(const void *addr)
 #define data_race(expr)                                                        \
 	({                                                                     \
 		typeof(({ expr; })) __val;                                     \
-		kcsan_nestable_atomic_begin();                                 \
+		kcsan_disable_current();                                       \
 		__val = ({ expr; });                                           \
-		kcsan_nestable_atomic_end();                                   \
+		kcsan_enable_current();                                        \
 		__val;                                                         \
 	})
 #else