Currently if we oops or warn while function_graph is active the stack
trace looks like:
.trace_graph_return+0xac/0x100
.ftrace_return_to_handler+0x98/0x140
.return_to_handler+0x20/0x40
.return_to_handler+0x0/0x40
.return_to_handler+0x0/0x40
.return_to_handler+0x0/0x40
.return_to_handler+0x0/0x40
.return_to_handler+0x0/0x40
.return_to_handler+0x0/0x40
.cpu_startup_entry+0x34/0x40
.start_secondary+0x680/0x6f0
start_secondary_prolog+0x10/0x14
Notice the multiple entries that just show .return_to_handler.
There is logic in show_stack() to detect this case and print the
traced function, but we inadvertently broke it in commit
7d56c65a6ff9 ("powerpc/ftrace: Remove mod_return_to_handler") (2014),
because that commit accidentally removed the dereference of rth which
gets the text address from the function descriptor. Hence this is only
broken on big endian (or technically ELFv1).
Fix it by using the proper accessor, which is ppc_function_entry().
Result is we get a stack trace such as:
.trace_graph_return+0x134/0x160
.ftrace_return_to_handler+0x94/0x140
.return_to_handler+0x20/0x40
.return_to_handler+0x0/0x40 (.shared_cede_loop+0x48/0x130)
.return_to_handler+0x0/0x40 (.cpuidle_enter_state+0xa0/0x690)
.return_to_handler+0x0/0x40 (.cpuidle_enter+0x44/0x70)
.return_to_handler+0x0/0x40 (.call_cpuidle+0x68/0xc0)
.return_to_handler+0x0/0x40 (.do_idle+0x37c/0x400)
.return_to_handler+0x0/0x40 (.cpu_startup_entry+0x30/0x50)
.rest_init+0x224/0x348
Fixes: 7d56c65a6ff9 ("powerpc/ftrace: Remove mod_return_to_handler")
Signed-off-by: Michael Ellerman <m...@ellerman.id.au>
---
arch/powerpc/kernel/process.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 8fc4de0d22b4..1601d7cfe45e 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -2048,7 +2048,7 @@ void show_stack(struct task_struct *tsk, unsigned long
*stack)
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
struct ftrace_ret_stack *ret_stack;
extern void return_to_handler(void);
- unsigned long rth = (unsigned long)return_to_handler;
+ unsigned long rth = ppc_function_entry(return_to_handler);
int curr_frame = 0;
#endif
--
2.21.0
