linux-kernel - [PATCH v10 03/11] arm64: Make get_wchan() use arch_stack

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Date:   Thu, 14 Oct 2021 21:58:39 -0500
From:   madvenka@...ux.microsoft.com
To:     mark.rutland@....com, broonie@...nel.org, jpoimboe@...hat.com,
        ardb@...nel.org, nobuta.keiya@...itsu.com,
        sjitindarsingh@...il.com, catalin.marinas@....com, will@...nel.org,
        jmorris@...ei.org, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        madvenka@...ux.microsoft.com
Subject: [PATCH v10 03/11] arm64: Make get_wchan() use arch_stack_walk()

From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>

Currently, get_wchan() in ARM64 code walks the stack using start_backtrace()
and unwind_frame(). Make it use arch_stack_walk() instead. This makes
maintenance easier.

Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
---
 arch/arm64/kernel/process.c | 38 ++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index c8989b999250..48ed89acce0d 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -544,11 +544,27 @@ __notrace_funcgraph struct task_struct *__switch_to(struct task_struct *prev,
 	return last;
 }
 
+struct wchan_info {
+	unsigned long	pc;
+	int		count;
+};
+
+static bool get_wchan_cb(void *arg, unsigned long pc)
+{
+	struct wchan_info *wchan_info = arg;
+
+	if (!in_sched_functions(pc)) {
+		wchan_info->pc = pc;
+		return false;
+	}
+	return wchan_info->count++ < 16;
+}
+
 unsigned long get_wchan(struct task_struct *p)
 {
-	struct stackframe frame;
-	unsigned long stack_page, ret = 0;
-	int count = 0;
+	unsigned long stack_page;
+	struct wchan_info wchan_info;
+
 	if (!p || p == current || task_is_running(p))
 		return 0;
 
@@ -556,20 +572,12 @@ unsigned long get_wchan(struct task_struct *p)
 	if (!stack_page)
 		return 0;
 
-	start_backtrace(&frame, thread_saved_fp(p), thread_saved_pc(p));
+	wchan_info.pc = 0;
+	wchan_info.count = 0;
+	arch_stack_walk(get_wchan_cb, &wchan_info, p, NULL);
 
-	do {
-		if (unwind_frame(p, &frame))
-			goto out;
-		if (!in_sched_functions(frame.pc)) {
-			ret = frame.pc;
-			goto out;
-		}
-	} while (count++ < 16);
-
-out:
 	put_task_stack(p);
-	return ret;
+	return wchan_info.pc;
 }
 
 unsigned long arch_align_stack(unsigned long sp)
-- 
2.25.1