x86: Pin task-stack in __get_wchan()

mainline inclusion
from mainline-v5.16-rc2
commit 0dc636b3
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5BKYL


CVE: NA

--------------------------------

When commit 5d1ceb39 ("x86: Fix __get_wchan() for !STACKTRACE")
moved from stacktrace to native unwind_*() usage, the
try_get_task_stack() got lost, leading to use-after-free issues for
dying tasks.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixes: 5d1ceb39 ("x86: Fix __get_wchan() for !STACKTRACE")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215031
Link: https://lore.kernel.org/stable/YZV02RCRVHIa144u@fedora64.linuxtx.org/


Reported-by: Justin Forbes <jmforbes@linuxtx.org>
Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Lin Yujun <linyujun809@huawei.com>
Reviewed-by: Zhang Jianhua <chris.zjh@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>