Provide ksw_stack_init() and ksw_stack_exit() to manage entry and
exit probes for the target function from ksw_get_config().

The entry/exit probe handlers use atomic ksw_stack_pid to ensure a
singleton watch and current->kstackwatch_ctx.depth to track
recursion depth. A watch is set up only when depth reaches the
configured value.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 mm/kstackwatch/kstackwatch.h |   4 ++
 mm/kstackwatch/stack.c       | 113 +++++++++++++++++++++++++++++++++++
 2 files changed, 117 insertions(+)

diff --git a/mm/kstackwatch/kstackwatch.h b/mm/kstackwatch/kstackwatch.h
index 0786fa961011..5ea2db76cdfb 100644
--- a/mm/kstackwatch/kstackwatch.h
+++ b/mm/kstackwatch/kstackwatch.h
@@ -38,6 +38,10 @@ struct ksw_config {
 // singleton, only modified in kernel.c
 const struct ksw_config *ksw_get_config(void);
 
+/* stack management */
+int ksw_stack_init(void);
+void ksw_stack_exit(void);
+
 /* watch management */
 int ksw_watch_init(void);
 void ksw_watch_exit(void);
diff --git a/mm/kstackwatch/stack.c b/mm/kstackwatch/stack.c
index cec594032515..ac52a9f81486 100644
--- a/mm/kstackwatch/stack.c
+++ b/mm/kstackwatch/stack.c
@@ -1 +1,114 @@
 // SPDX-License-Identifier: GPL-2.0
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/atomic.h>
+#include <linux/fprobe.h>
+#include <linux/kprobes.h>
+#include <linux/kstackwatch_types.h>
+#include <linux/printk.h>
+
+#include "kstackwatch.h"
+
+static struct kprobe entry_probe;
+static struct fprobe exit_probe;
+#define INVALID_PID -1
+static atomic_t ksw_stack_pid = ATOMIC_INIT(INVALID_PID);
+
+static int ksw_stack_prepare_watch(struct pt_regs *regs,
+				   const struct ksw_config *config,
+				   ulong *watch_addr, u16 *watch_len)
+{
+	/* implement logic will be added in following patches */
+	*watch_addr = 0;
+	*watch_len = 0;
+	return 0;
+}
+
+static void ksw_stack_entry_handler(struct kprobe *p, struct pt_regs *regs,
+				    unsigned long flags)
+{
+	struct kstackwatch_ctx *ctx = &current->kstackwatch_ctx;
+	ulong watch_addr;
+	u16 watch_len;
+	int ret;
+
+	if (ctx->depth++ != ksw_get_config()->depth)
+		return;
+
+	if (atomic_cmpxchg(&ksw_stack_pid, INVALID_PID, current->pid) !=
+	    INVALID_PID)
+		return;
+
+	ret = ksw_stack_prepare_watch(regs, ksw_get_config(), &watch_addr,
+				      &watch_len);
+	if (ret) {
+		atomic_set(&ksw_stack_pid, INVALID_PID);
+		pr_err("failed to prepare watch target: %d\n", ret);
+		return;
+	}
+
+	ret = ksw_watch_on(watch_addr, watch_len);
+	if (ret) {
+		atomic_set(&ksw_stack_pid, INVALID_PID);
+		pr_err("failed to watch on depth:%d addr:0x%lx len:%u %d\n",
+		       ksw_get_config()->depth, watch_addr, watch_len, ret);
+		return;
+	}
+
+	ctx->watch_addr = watch_addr;
+	ctx->watch_len = watch_len;
+	ctx->watch_on = true;
+}
+
+static void ksw_stack_exit_handler(struct fprobe *fp, unsigned long ip,
+				   unsigned long ret_ip,
+				   struct ftrace_regs *regs, void *data)
+{
+	struct kstackwatch_ctx *ctx = &current->kstackwatch_ctx;
+
+	if (--ctx->depth != ksw_get_config()->depth)
+		return;
+
+	if (atomic_read(&ksw_stack_pid) != current->pid)
+		return;
+	WARN_ON_ONCE(!ctx->watch_on);
+	WARN_ON_ONCE(ksw_watch_off(ctx->watch_addr, ctx->watch_len));
+	ctx->watch_on = false;
+
+	atomic_set(&ksw_stack_pid, INVALID_PID);
+}
+
+int ksw_stack_init(void)
+{
+	int ret;
+	char *symbuf = NULL;
+
+	memset(&entry_probe, 0, sizeof(entry_probe));
+	entry_probe.symbol_name = ksw_get_config()->function;
+	entry_probe.offset = ksw_get_config()->ip_offset;
+	entry_probe.post_handler = ksw_stack_entry_handler;
+	ret = register_kprobe(&entry_probe);
+	if (ret) {
+		pr_err("Failed to register kprobe ret %d\n", ret);
+		return ret;
+	}
+
+	memset(&exit_probe, 0, sizeof(exit_probe));
+	exit_probe.exit_handler = ksw_stack_exit_handler;
+	symbuf = (char *)ksw_get_config()->function;
+
+	ret = register_fprobe_syms(&exit_probe, (const char **)&symbuf, 1);
+	if (ret < 0) {
+		pr_err("register_fprobe_syms fail %d\n", ret);
+		unregister_kprobe(&entry_probe);
+		return ret;
+	}
+
+	return 0;
+}
+
+void ksw_stack_exit(void)
+{
+	unregister_fprobe(&exit_probe);
+	unregister_kprobe(&entry_probe);
+}
-- 
2.43.0