Merge tag 'kcsan.2022.01.09a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Pull KCSAN updates from Paul McKenney:
 "This provides KCSAN fixes and also the ability to take memory barriers
  into account for weakly-ordered systems. This last can increase the
  probability of detecting certain types of data races"

* tag 'kcsan.2022.01.09a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (29 commits)
  kcsan: Only test clear_bit_unlock_is_negative_byte if arch defines it
  kcsan: Avoid nested contexts reading inconsistent reorder_access
  kcsan: Turn barrier instrumentation into macros
  kcsan: Make barrier tests compatible with lockdep
  kcsan: Support WEAK_MEMORY with Clang where no objtool support exists
  compiler_attributes.h: Add __disable_sanitizer_instrumentation
  objtool, kcsan: Remove memory barrier instrumentation from noinstr
  objtool, kcsan: Add memory barrier instrumentation to whitelist
  sched, kcsan: Enable memory barrier instrumentation
  mm, kcsan: Enable barrier instrumentation
  x86/qspinlock, kcsan: Instrument barrier of pv_queued_spin_unlock()
  x86/barriers, kcsan: Use generic instrumentation for non-smp barriers
  asm-generic/bitops, kcsan: Add instrumentation for barriers
  locking/atomics, kcsan: Add instrumentation for barriers
  locking/barriers, kcsan: Support generic instrumentation
  locking/barriers, kcsan: Add instrumentation for barriers
  kcsan: selftest: Add test case to check memory barrier instrumentation
  kcsan: Ignore GCC 11+ warnings about TSan runtime support
  kcsan: test: Add test cases for memory barrier instrumentation
  kcsan: test: Match reordered or normal accesses
  ...

3 files changed, 50 insertions, 11 deletions

diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
index 37cb504c77e1..19f693b68a96 100644
--- a/scripts/Makefile.kcsan
+++ b/scripts/Makefile.kcsan
@@ -9,7 +9,18 @@ endif
 
 # Keep most options here optional, to allow enabling more compilers if absence
 # of some options does not break KCSAN nor causes false positive reports.
-export CFLAGS_KCSAN := -fsanitize=thread \
-	$(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \
+kcsan-cflags := -fsanitize=thread -fno-optimize-sibling-calls \
 	$(call cc-option,$(call cc-param,tsan-compound-read-before-write=1),$(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1))) \
 	$(call cc-param,tsan-distinguish-volatile=1)
+
+ifdef CONFIG_CC_IS_GCC
+# GCC started warning about operations unsupported by the TSan runtime. But
+# KCSAN != TSan, so just ignore these warnings.
+kcsan-cflags += -Wno-tsan
+endif
+
+ifndef CONFIG_KCSAN_WEAK_MEMORY
+kcsan-cflags += $(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0))
+endif
+
+export CFLAGS_KCSAN := $(kcsan-cflags)
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index d1f865b8c0cb..ab17f7b2e33c 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -182,6 +182,11 @@ ifeq ($(CONFIG_KCSAN),y)
 _c_flags += $(if $(patsubst n%,, \
 	$(KCSAN_SANITIZE_$(basetarget).o)$(KCSAN_SANITIZE)y), \
 	$(CFLAGS_KCSAN))
+# Some uninstrumented files provide implied barriers required to avoid false
+# positives: set KCSAN_INSTRUMENT_BARRIERS for barrier instrumentation only.
+_c_flags += $(if $(patsubst n%,, \
+	$(KCSAN_INSTRUMENT_BARRIERS_$(basetarget).o)$(KCSAN_INSTRUMENT_BARRIERS)n), \
+	-D__KCSAN_INSTRUMENT_BARRIERS__)
 endif
 
 # $(srctree)/$(src) for including checkin headers from generated source files
diff --git a/scripts/atomic/gen-atomic-instrumented.sh b/scripts/atomic/gen-atomic-instrumented.sh
index 035ceb4ee85c..68f902731d01 100755
--- a/scripts/atomic/gen-atomic-instrumented.sh
+++ b/scripts/atomic/gen-atomic-instrumented.sh
@@ -34,6 +34,14 @@ gen_param_check()
 gen_params_checks()
 {
 	local meta="$1"; shift
+	local order="$1"; shift
+
+	if [ "${order}" = "_release" ]; then
+		printf "\tkcsan_release();\n"
+	elif [ -z "${order}" ] && ! meta_in "$meta" "slv"; then
+		# RMW with return value is fully ordered
+		printf "\tkcsan_mb();\n"
+	fi
 
 	while [ "$#" -gt 0 ]; do
 		gen_param_check "$meta" "$1"
@@ -56,7 +64,7 @@ gen_proto_order_variant()
 
 	local ret="$(gen_ret_type "${meta}" "${int}")"
 	local params="$(gen_params "${int}" "${atomic}" "$@")"
-	local checks="$(gen_params_checks "${meta}" "$@")"
+	local checks="$(gen_params_checks "${meta}" "${order}" "$@")"
 	local args="$(gen_args "$@")"
 	local retstmt="$(gen_ret_stmt "${meta}")"
 
@@ -75,29 +83,44 @@ EOF
 gen_xchg()
 {
 	local xchg="$1"; shift
+	local order="$1"; shift
 	local mult="$1"; shift
 
+	kcsan_barrier=""
+	if [ "${xchg%_local}" = "${xchg}" ]; then
+		case "$order" in
+		_release)	kcsan_barrier="kcsan_release()" ;;
+		"")			kcsan_barrier="kcsan_mb()" ;;
+		esac
+	fi
+
 	if [ "${xchg%${xchg#try_cmpxchg}}" = "try_cmpxchg" ] ; then
 
 cat <<EOF
-#define ${xchg}(ptr, oldp, ...) \\
+#define ${xchg}${order}(ptr, oldp, ...) \\
 ({ \\
 	typeof(ptr) __ai_ptr = (ptr); \\
 	typeof(oldp) __ai_oldp = (oldp); \\
+EOF
+[ -n "$kcsan_barrier" ] && printf "\t${kcsan_barrier}; \\\\\n"
+cat <<EOF
 	instrument_atomic_write(__ai_ptr, ${mult}sizeof(*__ai_ptr)); \\
 	instrument_atomic_write(__ai_oldp, ${mult}sizeof(*__ai_oldp)); \\
-	arch_${xchg}(__ai_ptr, __ai_oldp, __VA_ARGS__); \\
+	arch_${xchg}${order}(__ai_ptr, __ai_oldp, __VA_ARGS__); \\
 })
 EOF
 
 	else
 
 cat <<EOF
-#define ${xchg}(ptr, ...) \\
+#define ${xchg}${order}(ptr, ...) \\
 ({ \\
 	typeof(ptr) __ai_ptr = (ptr); \\
+EOF
+[ -n "$kcsan_barrier" ] && printf "\t${kcsan_barrier}; \\\\\n"
+cat <<EOF
 	instrument_atomic_write(__ai_ptr, ${mult}sizeof(*__ai_ptr)); \\
-	arch_${xchg}(__ai_ptr, __VA_ARGS__); \\
+	arch_${xchg}${order}(__ai_ptr, __VA_ARGS__); \\
 })
 EOF
 
@@ -145,21 +168,21 @@ done
 
 for xchg in "xchg" "cmpxchg" "cmpxchg64" "try_cmpxchg"; do
 	for order in "" "_acquire" "_release" "_relaxed"; do
-		gen_xchg "${xchg}${order}" ""
+		gen_xchg "${xchg}" "${order}" ""
 		printf "\n"
 	done
 done
 
 for xchg in "cmpxchg_local" "cmpxchg64_local" "sync_cmpxchg"; do
-	gen_xchg "${xchg}" ""
+	gen_xchg "${xchg}" "" ""
 	printf "\n"
 done
 
-gen_xchg "cmpxchg_double" "2 * "
+gen_xchg "cmpxchg_double" "" "2 * "
 
 printf "\n\n"
 
-gen_xchg "cmpxchg_double_local" "2 * "
+gen_xchg "cmpxchg_double_local" "" "2 * "
 
 cat <<EOF