Date:   Tue, 30 Nov 2021 12:44:28 +0100
In-Reply-To: <20211130114433.2580590-1-elver@google.com>
Message-Id: <20211130114433.2580590-21-elver@google.com>
Mime-Version: 1.0
References: <20211130114433.2580590-1-elver@google.com>
Subject: [PATCH v3 20/25] mm, kcsan: Enable barrier instrumentation
From:   Marco Elver <elver@google.com>
To:     elver@google.com, "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Alexander Potapenko <glider@google.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Dmitry Vyukov <dvyukov@google.com>,
        Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Waiman Long <longman@redhat.com>,
        Will Deacon <will@kernel.org>, kasan-dev@googlegroups.com,
        linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, llvm@lists.linux.dev, x86@kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Some memory management calls imply memory barriers that are required to
avoid false positives. For example, without the correct instrumentation,
we could observe data races of the following variant:

                   T0           |           T1
        ------------------------+------------------------
                                |
         *a = 42;    ---+       |
         kfree(a);      |       |
                        |       | b = kmalloc(..); // b == a
          <reordered> <-+       | *b = 42;         // not a data race!
                                |

Therefore, instrument memory barriers in all allocator code currently
not being instrumented in a default build.

Signed-off-by: Marco Elver <elver@google.com>
---
 mm/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/Makefile b/mm/Makefile
index d6c0042e3aa0..7919cd7f13f2 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -15,6 +15,8 @@ KCSAN_SANITIZE_slab_common.o := n
 KCSAN_SANITIZE_slab.o := n
 KCSAN_SANITIZE_slub.o := n
 KCSAN_SANITIZE_page_alloc.o := n
+# But enable explicit instrumentation for memory barriers.
+KCSAN_INSTRUMENT_BARRIERS := y
 
 # These files are disabled because they produce non-interesting and/or
 # flaky coverage that is not a function of syscall inputs. E.g. slab is out of
-- 
2.34.0.rc2.393.gf8c9666880-goog