Merge branch 'kcsan' of git://git.kernel.org/pub/scm/linux/kernel/git…

…/paulmck/linux-rcu into locking/core

Pull v5.9 KCSAN bits from Paul E. McKenney.

Perhaps the most important change is that GCC 11 now has all fixes in place
to support KCSAN, so GCC support can be enabled again.

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

Documentation/dev-tools/kcsan.rst

@@ -8,7 +8,8 @@ approach to detect races. KCSAN's primary purpose is to detect `data races`_.
 Usage
 -----
 
-KCSAN requires Clang version 11 or later.
+KCSAN is supported by both GCC and Clang. With GCC we require version 11 or
+later, and with Clang also require version 11 or later.
 
 To enable KCSAN configure the kernel with::
 

arch/x86/mm/pat/set_memory.c

@@ -135,7 +135,7 @@ static inline void cpa_inc_2m_checked(void)
 
 static inline void cpa_inc_4k_install(void)
 {
-	cpa_4k_install++;
+	data_race(cpa_4k_install++);
 }
 
 static inline void cpa_inc_lp_sameprot(int level)

include/linux/rculist.h

@@ -248,6 +248,8 @@ static inline void __list_splice_init_rcu(struct list_head *list,
 	 */
 
 	sync();
+	ASSERT_EXCLUSIVE_ACCESS(*first);
+	ASSERT_EXCLUSIVE_ACCESS(*last);
 
 	/*
 	 * Readers are finished with the source list, so perform splice.

kernel/fork.c

@@ -359,7 +359,13 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 
 	if (new) {
-		*new = *orig;
+		ASSERT_EXCLUSIVE_WRITER(orig->vm_flags);
+		ASSERT_EXCLUSIVE_WRITER(orig->vm_file);
+		/*
+		 * orig->shared.rb may be modified concurrently, but the clone
+		 * will be reinitialized.
+		 */
+		*new = data_race(*orig);
 		INIT_LIST_HEAD(&new->anon_vma_chain);
 		new->vm_next = new->vm_prev = NULL;
 	}

kernel/kcsan/Makefile

@@ -7,8 +7,11 @@ CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE)
 
-CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
-	$(call cc-option,-fno-stack-protector,)
+CFLAGS_core.o := $(call cc-option,-fno-conserve-stack) \
+	-fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
 obj-y := core.o debugfs.o report.o
-obj-$(CONFIG_KCSAN_SELFTEST) += test.o
+obj-$(CONFIG_KCSAN_SELFTEST) += selftest.o
+
+CFLAGS_kcsan-test.o := $(CFLAGS_KCSAN) -g -fno-omit-frame-pointer
+obj-$(CONFIG_KCSAN_TEST) += kcsan-test.o

kernel/kcsan/atomic.h

@@ -3,8 +3,7 @@
 #ifndef _KERNEL_KCSAN_ATOMIC_H
 #define _KERNEL_KCSAN_ATOMIC_H
 
-#include <linux/jiffies.h>
-#include <linux/sched.h>
+#include <linux/types.h>
 
 /*
  * Special rules for certain memory where concurrent conflicting accesses are
@@ -13,8 +12,7 @@
  */
 static bool kcsan_is_atomic_special(const volatile void *ptr)
 {
-	/* volatile globals that have been observed in data races. */
-	return ptr == &jiffies || ptr == &current->state;
+	return false;
 }
 
 #endif /* _KERNEL_KCSAN_ATOMIC_H */

kernel/kcsan/core.c

@@ -776,6 +776,7 @@ EXPORT_SYMBOL(__kcsan_check_access);
  */
 
 #define DEFINE_TSAN_READ_WRITE(size)                                           \
+	void __tsan_read##size(void *ptr);                                     \
 	void __tsan_read##size(void *ptr)                                      \
 	{                                                                      \
 		check_access(ptr, size, 0);                                    \
@@ -784,6 +785,7 @@ EXPORT_SYMBOL(__kcsan_check_access);
 	void __tsan_unaligned_read##size(void *ptr)                            \
 		__alias(__tsan_read##size);                                    \
 	EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
+	void __tsan_write##size(void *ptr);                                    \
 	void __tsan_write##size(void *ptr)                                     \
 	{                                                                      \
 		check_access(ptr, size, KCSAN_ACCESS_WRITE);                   \
@@ -799,12 +801,14 @@ DEFINE_TSAN_READ_WRITE(4);
 DEFINE_TSAN_READ_WRITE(8);
 DEFINE_TSAN_READ_WRITE(16);
 
+void __tsan_read_range(void *ptr, size_t size);
 void __tsan_read_range(void *ptr, size_t size)
 {
 	check_access(ptr, size, 0);
 }
 EXPORT_SYMBOL(__tsan_read_range);
 
+void __tsan_write_range(void *ptr, size_t size);
 void __tsan_write_range(void *ptr, size_t size)
 {
 	check_access(ptr, size, KCSAN_ACCESS_WRITE);
@@ -821,6 +825,7 @@ EXPORT_SYMBOL(__tsan_write_range);
  * the size-check of compiletime_assert_rwonce_type().
  */
 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size)                                  \
+	void __tsan_volatile_read##size(void *ptr);                            \
 	void __tsan_volatile_read##size(void *ptr)                             \
 	{                                                                      \
 		const bool is_atomic = size <= sizeof(long long) &&            \
@@ -833,6 +838,7 @@ EXPORT_SYMBOL(__tsan_write_range);
 	void __tsan_unaligned_volatile_read##size(void *ptr)                   \
 		__alias(__tsan_volatile_read##size);                           \
 	EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size);                   \
+	void __tsan_volatile_write##size(void *ptr);                           \
 	void __tsan_volatile_write##size(void *ptr)                            \
 	{                                                                      \
 		const bool is_atomic = size <= sizeof(long long) &&            \
@@ -858,14 +864,17 @@ DEFINE_TSAN_VOLATILE_READ_WRITE(16);
  * The below are not required by KCSAN, but can still be emitted by the
  * compiler.
  */
+void __tsan_func_entry(void *call_pc);
 void __tsan_func_entry(void *call_pc)
 {
 }
 EXPORT_SYMBOL(__tsan_func_entry);
+void __tsan_func_exit(void);
 void __tsan_func_exit(void)
 {
 }
 EXPORT_SYMBOL(__tsan_func_exit);
+void __tsan_init(void);
 void __tsan_init(void)
 {
 }