R状态的任务为什么/proc/[pid]/stack堆栈不准 ?

cpu高，R状态的任务为什么/proc/[pid]/stack堆栈不准

构造sys cpu高R的情况，为什么堆栈不准
190         read_unlock(&tasklist_lock);
191 while(1) {
192                 udelay(8000);
193                 usleep_range(1, 2);
194 }
195
196         return 0;
197 }

如下，只有在任务睡眠的时候堆栈是正确的
1、原因是如果任务在运行，cat stack的起始帧是上次切换出去的时候ENTRY(cpu_switch_to)保存的帧
而如果任务在运行处于R状态，那么用上次的起始帧去unwind现在的内核栈，回溯就会有很奇怪的数据，不是正常的数据
2、如果是单核的情况，那么在敲回溯的时候，R状态的任务会被preempt 调度出去，这种情况下cat的stack每次都是准确的
3、如果是用户态100%的情况rtprocess_arm64 1 50 2（FIFO 50 cpu2），内核栈是退出来的已经清空了的，一般没有内容
 # cat /proc/189/stack
[<0>] __switch_to+0x288/0x418
/ #


/ # cat /proc/148/stack
[<0>] __switch_to+0x288/0x418
[<0>] info_show+0x23c/0x2b8
[<0>] seq_read+0x334/0xf38
[<0>] proc_reg_read+0x124/0x1b0
[<0>] do_iter_read+0x2e8/0x490
[<0>] vfs_readv+0xc8/0x120
[<0>] default_file_splice_read+0x374/0x730
[<0>] do_splice_to+0xe0/0x140
[<0>] splice_direct_to_actor+0x270/0x720
[<0>] do_splice_direct+0x12c/0x200
[<0>] do_sendfile+0x338/0xac0
[<0>] __arm64_sys_sendfile64+0x340/0x400
[<0>] el0_svc_common.constprop.0+0x110/0x378
[<0>] el0_svc_handler+0x4c/0xd0
[<0>] el0_svc+0x8/0x1bc
/ # cat /proc/148/stack
[<0>] __switch_to+0x288/0x418
[<0>] 0xffff000008cccc00
/ # cat /proc/148/stack
[<0>] __switch_to+0x288/0x418
[<0>] str_spec.71612+0x1c2838/0x2d6378
/ # cat /proc/148/stack
[<0>] __switch_to+0x288/0x418
[<0>] str_spec.71612+0x1c2838/0x2d6378
/ #

if (tsk != current) {
    start_backtrace(&frame, thread_saved_fp(tsk),
        thread_saved_pc(tsk));

#define thread_saved_pc(tsk)    \
    ((unsigned long)(tsk->thread.cpu_context.pc))
#define thread_saved_sp(tsk)    \
    ((unsigned long)(tsk->thread.cpu_context.sp))
#define thread_saved_fp(tsk)    \
    ((unsigned long)(tsk->thread.cpu_context.fp))


1208 */
1209 ENTRY(cpu_switch_to)
1210         mov     x10, #THREAD_CPU_CONTEXT
1211         add     x8, x0, x10
1212         mov     x9, sp
1213         stp     x19, x20, [x8], #16 // store callee-saved registers
1214         stp     x21, x22, [x8], #16
1215         stp     x23, x24, [x8], #16
1216         stp     x25, x26, [x8], #16
1217         stp     x27, x28, [x8], #16
1218         stp     x29, x9, [x8], #16
1219         str     lr, [x8]
1220         add     x8, x1, x10
1221         ldp     x19, x20, [x8], #16 // restore callee-saved registers
1222         ldp     x21, x22, [x8], #16
1223         ldp     x23, x24, [x8], #16
1224         ldp     x25, x26, [x8], #16
1225         ldp     x27, x28, [x8], #16
1226         ldp     x29, x9, [x8], #16
1227         ldr     lr, [x8]
1228         mov     sp, x9
1229         msr     sp_el0, x1
1230         ret
1231 ENDPROC(cpu_switch_to)
1232 NOKPROBE(cpu_switch_to)