[PATCH v10 07/11] arm64: Call stack_backtrace() only from within walk_stackframe()

madvenka
2021-10-15T02:59:24Z

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

Currently, arch_stack_walk() calls start_backtrace() and walk_stackframe()
separately. There is no need to do that. Instead, call start_backtrace()
from within walk_stackframe(). In other words, walk_stackframe() is the only
unwind function a consumer needs to call.

Currently, the only consumer is arch_stack_walk(). In the future,
arch_stack_walk_reliable() will be another consumer.

start_backtrace(), unwind_frame() and walk_stackframe() are only used
within arm64/kernel/stacktrace.c. Make them static and remove them from
arch/arm64/include/asm/stacktrace.h.

Currently, there is a check for a NULL task in unwind_frame(). It is not
needed since all current consumers pass a non-NULL task.

Use struct stackframe only within the unwind functions.

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
arch/arm64/include/asm/stacktrace.h | 6 ----
arch/arm64/kernel/stacktrace.c | 51 ++++++++++++++++-------------
2 files changed, 29 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
index 8aebc00c1718..c239f357d779 100644
--- a/arch/arm64/include/asm/stacktrace.h
+++ b/arch/arm64/include/asm/stacktrace.h
@@ -61,9 +61,6 @@ struct stackframe {
#endif
};

-extern int unwind_frame(struct task_struct *tsk, struct stackframe *frame);
-extern void walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
- bool (*fn)(void *, unsigned long), void *data);
extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
const char *loglvl);

@@ -148,7 +145,4 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
return false;
}

-void start_backtrace(struct stackframe *frame, unsigned long fp,
- unsigned long pc);
-
#endif /* __ASM_STACKTRACE_H */
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 776c4debb5a7..7d32cee9ef4b 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -33,8 +33,8 @@
*/

-void start_backtrace(struct stackframe *frame, unsigned long fp,
- unsigned long pc)
+static void start_backtrace(struct stackframe *frame, unsigned long fp,
+ unsigned long pc)
{
frame->fp = fp;
frame->pc = pc;
@@ -63,14 +63,12 @@ void start_backtrace(struct stackframe *frame, unsigned long fp,
* records (e.g. a cycle), determined based on the location and fp value of A
* and the location (but not the fp value) of B.
*/
-int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
+static int notrace unwind_frame(struct task_struct *tsk,
+ struct stackframe *frame)
{
unsigned long fp = frame->fp;
struct stack_info info;

- if (!tsk)
- tsk = current;
-
/* Final frame; nothing to unwind */
if (fp == (unsigned long)task_pt_regs(tsk)->stackframe)
return -ENOENT;
@@ -136,15 +134,21 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
}
NOKPROBE_SYMBOL(unwind_frame);

-void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
- bool (*fn)(void *, unsigned long), void *data)
+static void notrace walk_stackframe(struct task_struct *tsk,
+ unsigned long fp, unsigned long pc,
+ bool (*fn)(void *, unsigned long),
+ void *data)
{
+ struct stackframe frame;
+
+ start_backtrace(&frame, fp, pc);
+
while (1) {
int ret;

- if (!fn(data, frame->pc))
+ if (!fn(data, frame.pc))
break;
- ret = unwind_frame(tsk, frame);
+ ret = unwind_frame(tsk, &frame);
if (ret < 0)
break;
}
@@ -190,19 +194,22 @@ noinline notrace void arch_stack_walk(stack_trace_consume_fn consume_entry,
void *cookie, struct task_struct *task,
struct pt_regs *regs)
{
- struct stackframe frame;
+ unsigned long fp, pc;
+
+ if (regs) {
+ fp = regs->regs[29];
+ pc = regs->pc;
+ } else if (task == current) {
+ /* Skip arch_stack_walk() in the stack trace. */
+ fp = (unsigned long)__builtin_frame_address(1);
+ pc = (unsigned long)__builtin_return_address(0);
+ } else {
+ /* Caller guarantees that the task is not running. */
+ fp = thread_saved_fp(task);
+ pc = thread_saved_pc(task);
+ }
+ walk_stackframe(task, fp, pc, consume_entry, cookie);

- if (regs)
- start_backtrace(&frame, regs->regs[29], regs->pc);
- else if (task == current)
- start_backtrace(&frame,
- (unsigned long)__builtin_frame_address(1),
- (unsigned long)__builtin_return_address(0));
- else
- start_backtrace(&frame, thread_saved_fp(task),
- thread_saved_pc(task));
-
- walk_stackframe(task, &frame, consume_entry, cookie);
}

#endif
--
2.25.1