@@ -23,6 +23,7 @@
#include <linux/tick.h>
#include <linux/reboot.h>
#include <linux/fs.h>
+#include <linux/ftrace.h>
#include <linux/preempt.h>
#include <asm/uaccess.h>
#include <asm/mmu_context.h>
@@ -264,8 +265,8 @@ static void ubc_set_tracing(int asid, unsigned long pc)
* switch_to(x,y) should switch tasks from x to y.
*
*/
-struct task_struct *__switch_to(struct task_struct *prev,
- struct task_struct *next)
+__notrace_funcgraph struct task_struct *
+__switch_to(struct task_struct *prev, struct task_struct *next)
{
#if defined(CONFIG_SH_FPU)
unlazy_fpu(prev, task_pt_regs(prev));
Annotate __switch_to() so that the function graph tracer does not try to trace it. Use __notrace_funcgraph, as opposed to notrace, so that other tracers can continue to trace __switch_to(). The reason that we don't want to trace __switch_to() with the function graph tracer is because of how the return address stack in task_struct is implemented. When we enter __switch_to we store the real return address on prev's ret_stack. When we return from __switch_to() we've patched the return address on the kernel stack to be return_to_handler. Calling return_to_handler we do, -> ftrace_return_to_handler() -> ftrace_pop_return_ftrace() Which tries to pop the real return address from current->ret_stack. The problem being that we stored the return address on prev->ret_stack, but current now points to next, and next->ret_stack doesn't contain the correct return address (and is possibly even empty). Signed-off-by: Matt Fleming <matt@console-pimps.org> --- arch/sh/kernel/process_32.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-)