[PATCH] riscv: stacktrace: Fix missing the first frame

[Liu Shixin]

When running kfence_test, I found some testcases failed like this:

 # test_out_of_bounds_read: EXPECTATION FAILED at mm/kfence/kfence_test.c:346
 Expected report_matches(&expect) to be true, but is false
 not ok 1 - test_out_of_bounds_read

The corresponding call-trace is:

 BUG: KFENCE: out-of-bounds read in kunit_try_run_case+0x38/0x84

 Out-of-bounds read at 0x(____ptrval____) (32B right of kfence-#10):
  kunit_try_run_case+0x38/0x84
  kunit_generic_run_threadfn_adapter+0x12/0x1e
  kthread+0xc8/0xde
  ret_from_exception+0x0/0xc

The kfence_test using the first frame of call trace to check whether the
testcase is succeed or not. Patch a7c5c7e8ff78 skip first frame for all
case, which results the kfence_test failed. Indeed, we only need to skip
the first frame for case (task==NULL || task==current).

With this patch, the call-trace will be:

 BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0x88/0x19e

 Out-of-bounds read at 0x(____ptrval____) (1B left of kfence-#7):
  test_out_of_bounds_read+0x88/0x19e
  kunit_try_run_case+0x38/0x84
  kunit_generic_run_threadfn_adapter+0x12/0x1e
  kthread+0xc8/0xde
  ret_from_exception+0x0/0xc

Fixes: a7c5c7e8ff78 ("riscv: eliminate unreliable __builtin_frame_address(1)")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
 arch/riscv/kernel/stacktrace.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 08d11a53f39e..5fe2ae4cf135 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -30,6 +30,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 		fp = (unsigned long)__builtin_frame_address(0);
 		sp = current_stack_pointer;
 		pc = (unsigned long)walk_stackframe;
+		level = -1;
 	} else {
 		/* task blocked in __switch_to */
 		fp = task->thread.s[0];
@@ -41,7 +42,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 		unsigned long low, high;
 		struct stackframe *frame;
 
-		if (unlikely(!__kernel_text_address(pc) || (level++ >= 1 && !fn(arg, pc))))
+		if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, pc))))
 			break;
 
 		/* Validate frame pointer */
-- 
2.25.1