Rebase locking/kcsan to locking/urgent

Merge the state of the locking kcsan branch before the read/write_once()
and the atomics modifications got merged.

Squash the fallout of the rebase on top of the read/write once and atomic
fallback work into the merge. The history of the original branch is
preserved in tag locking-kcsan-2020-06-02.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 59 insertions, 0 deletions

diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h
new file mode 100644
index 000000000000..53340d8789f9
--- /dev/null
+++ b/include/linux/kcsan.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_KCSAN_H
+#define _LINUX_KCSAN_H
+
+#include <linux/kcsan-checks.h>
+#include <linux/types.h>
+
+#ifdef CONFIG_KCSAN
+
+/*
+ * Context for each thread of execution: for tasks, this is stored in
+ * task_struct, and interrupts access internal per-CPU storage.
+ */
+struct kcsan_ctx {
+	int disable_count; /* disable counter */
+	int atomic_next; /* number of following atomic ops */
+
+	/*
+	 * We distinguish between: (a) nestable atomic regions that may contain
+	 * other nestable regions; and (b) flat atomic regions that do not keep
+	 * track of nesting. Both (a) and (b) are entirely independent of each
+	 * other, and a flat region may be started in a nestable region or
+	 * vice-versa.
+	 *
+	 * This is required because, for example, in the annotations for
+	 * seqlocks, we declare seqlock writer critical sections as (a) nestable
+	 * atomic regions, but reader critical sections as (b) flat atomic
+	 * regions, but have encountered cases where seqlock reader critical
+	 * sections are contained within writer critical sections (the opposite
+	 * may be possible, too).
+	 *
+	 * To support these cases, we independently track the depth of nesting
+	 * for (a), and whether the leaf level is flat for (b).
+	 */
+	int atomic_nest_count;
+	bool in_flat_atomic;
+
+	/*
+	 * Access mask for all accesses if non-zero.
+	 */
+	unsigned long access_mask;
+
+	/* List of scoped accesses. */
+	struct list_head scoped_accesses;
+};
+
+/**
+ * kcsan_init - initialize KCSAN runtime
+ */
+void kcsan_init(void);
+
+#else /* CONFIG_KCSAN */
+
+static inline void kcsan_init(void)			{ }
+
+#endif /* CONFIG_KCSAN */
+
+#endif /* _LINUX_KCSAN_H */