Merge branch 'for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into locking/kcsan

Pull the KCSAN subsystem from Paul E. McKenney:

   "This pull request contains base kernel concurrency sanitizer
    (KCSAN) enablement for x86, courtesy of Marco Elver.  KCSAN is a
    sampling watchpoint-based data-race detector, and is documented in
    Documentation/dev-tools/kcsan.rst.  KCSAN was announced in September,
    and much feedback has since been incorporated:

      http://lkml.kernel.org/r/CANpmjNPJ_bHjfLZCAPV23AXFfiPiyXXqqu72n6TgWzb2Gnu1eA@mail.gmail.com

    The data races located thus far have resulted in a number of fixes:

      https://github.com/google/ktsan/wiki/KCSAN#upstream-fixes-of-data-races-found-by-kcsan

    Additional information may be found here:

      https://lore.kernel.org/lkml/20191114180303.66955-1-elver@google.com/
   "

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 49 insertions, 8 deletions

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 5e88e7e33abe..7d3e77781578 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -178,6 +178,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #endif
 
 #include <uapi/linux/types.h>
+#include <linux/kcsan-checks.h>
 
 #define __READ_ONCE_SIZE						\
 ({									\
@@ -193,12 +194,6 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 	}								\
 })
 
-static __always_inline
-void __read_once_size(const volatile void *p, void *res, int size)
-{
-	__READ_ONCE_SIZE;
-}
-
 #ifdef CONFIG_KASAN
 /*
  * We can't declare function 'inline' because __no_sanitize_address confilcts
@@ -207,18 +202,44 @@ void __read_once_size(const volatile void *p, void *res, int size)
  * '__maybe_unused' allows us to avoid defined-but-not-used warnings.
  */
 # define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
+# define __no_sanitize_or_inline __no_kasan_or_inline
 #else
 # define __no_kasan_or_inline __always_inline
 #endif
 
-static __no_kasan_or_inline
+#ifdef __SANITIZE_THREAD__
+/*
+ * Rely on __SANITIZE_THREAD__ instead of CONFIG_KCSAN, to avoid not inlining in
+ * compilation units where instrumentation is disabled.
+ */
+# define __no_kcsan_or_inline __no_sanitize_thread notrace __maybe_unused
+# define __no_sanitize_or_inline __no_kcsan_or_inline
+#else
+# define __no_kcsan_or_inline __always_inline
+#endif
+
+#ifndef __no_sanitize_or_inline
+#define __no_sanitize_or_inline __always_inline
+#endif
+
+static __no_kcsan_or_inline
+void __read_once_size(const volatile void *p, void *res, int size)
+{
+	kcsan_check_atomic_read(p, size);
+	__READ_ONCE_SIZE;
+}
+
+static __no_sanitize_or_inline
 void __read_once_size_nocheck(const volatile void *p, void *res, int size)
 {
 	__READ_ONCE_SIZE;
 }
 
-static __always_inline void __write_once_size(volatile void *p, void *res, int size)
+static __no_kcsan_or_inline
+void __write_once_size(volatile void *p, void *res, int size)
 {
+	kcsan_check_atomic_write(p, size);
+
 	switch (size) {
 	case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
 	case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
@@ -289,6 +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__ */
 
 /*