[tip: sched/core] x86: Fix get_wchan() to support the ORC unwinder

tip-bot2 for Qi Zheng
2021-10-15T09:45:22Z

The following commit has been merged into the sched/core branch of tip:

Commit-ID: bc9bbb81730ea667c31c5b284f95ee312bab466f
Gitweb: https://git.kernel.org/tip/bc9bbb81730ea667c31c5b284f95ee312bab466f
Author: Qi Zheng <zhengqi.arch@bytedance.com>
AuthorDate: Wed, 29 Sep 2021 15:02:17 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 15 Oct 2021 11:25:14 +02:00

x86: Fix get_wchan() to support the ORC unwinder

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 usually returned 0 regardless
of whether the task <pid> is running.

Reimplement 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 <zhengqi.arch@bytedance.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211008111626.271115116@infradead.org
---
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 1d9463e..e645925 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,