x86/unwind: Prevent false warnings for non-current tasks

mainline inclusion
from mainline-v5.7-rc5
commit b08418b5
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5BJD1


CVE: NA

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

There's some daring kernel code out there which dumps the stack of
another task without first making sure the task is inactive.  If the
task happens to be running while the unwinder is reading the stack,
unusual unwinder warnings can result.

There's no race-free way for the unwinder to know whether such a warning
is legitimate, so just disable unwinder warnings for all non-current
tasks.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Jones <dsj@fb.com>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: https://lore.kernel.org/r/ec424a2aea1d461eb30cab48a28c6433de2ab784.1587808742.git.jpoimboe@redhat.com


Signed-off-by: Yipeng Zou <zouyipeng@huawei.com>
Reviewed-by: Zhang Jianhua <chris.zjh@huawei.com>
Reviewed-by: Liao Chang <liaochang1@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>