Currently, the kernel CONFIG_UNWINDER_ORC option is enabled by
default on x86, but the implementation of get_wchan() is still
based on the frame pointer unwinder, so the /proc/<pid>/wchan
always return 0 regardless of whether the task <pid> is running.
We reimplement the get_wchan() by calling stack_trace_save_tsk(),
which is adapted to the ORC and frame pointer unwinders.
Fixes: ee9f8fce9964(x86/unwind: Add the ORC unwinder)
Signed-off-by: Qi Zheng <[email protected]>
---
Changlog in resend:
- rebase on next-20210830
In addition, this issue has existed for nearly 4 years and no one has
fixed it, maybe we can return 0 or remove this function directly if
nobody cares about the return value of the get_wchan() ?
The following is the previous patch link:
https://lore.kernel.org/patchwork/patch/1445013/
arch/x86/kernel/process.c | 51 +++--------------------------------------------
1 file changed, 3 insertions(+), 48 deletions(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1d9463e3096b..e645925f9f02 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -944,58 +944,13 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
*/
unsigned long get_wchan(struct task_struct *p)
{
- unsigned long start, bottom, top, sp, fp, ip, ret = 0;
- int count = 0;
+ unsigned long entry = 0;
if (p == current || task_is_running(p))
return 0;
- if (!try_get_task_stack(p))
- return 0;
-
- start = (unsigned long)task_stack_page(p);
- if (!start)
- goto out;
-
- /*
- * Layout of the stack page:
- *
- * ----------- topmax = start + THREAD_SIZE - sizeof(unsigned long)
- * PADDING
- * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING
- * stack
- * ----------- bottom = start
- *
- * The tasks stack pointer points at the location where the
- * framepointer is stored. The data on the stack is:
- * ... IP FP ... IP FP
- *
- * We need to read FP and IP, so we need to adjust the upper
- * bound by another unsigned long.
- */
- top = start + THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING;
- top -= 2 * sizeof(unsigned long);
- bottom = start;
-
- sp = READ_ONCE(p->thread.sp);
- if (sp < bottom || sp > top)
- goto out;
-
- fp = READ_ONCE_NOCHECK(((struct inactive_task_frame *)sp)->bp);
- do {
- if (fp < bottom || fp > top)
- goto out;
- ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
- if (!in_sched_functions(ip)) {
- ret = ip;
- goto out;
- }
- fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
- } while (count++ < 16 && !task_is_running(p));
-
-out:
- put_task_stack(p);
- return ret;
+ stack_trace_save_tsk(p, &entry, 1, 0);
+ return entry;
}
long do_arch_prctl_common(struct task_struct *task, int option,
--
2.11.0