mips: fix syscall_get_nr

stable inclusion
from stable-v5.10.173
commit 6c96c0b2e32661b2da11d4eab9c895336b2e9680
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8BFR3

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6c96c0b2e32661b2da11d4eab9c895336b2e9680

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

commit 85cc91e2 upstream.

The implementation of syscall_get_nr on mips used to ignore the task
argument and return the syscall number of the calling thread instead of
the target thread.

The bug was exposed to user space by commit 201766a2 ("ptrace: add
PTRACE_GET_SYSCALL_INFO request") and detected by strace test suite.

Link: https://github.com/strace/strace/issues/235


Fixes: c2d9f177 ("MIPS: Fix syscall_get_nr for the syscall exit tracing.")
Cc: <stable@vger.kernel.org> # v3.19+
Co-developed-by: Dmitry V. Levin <ldv@strace.io>
Signed-off-by: Dmitry V. Levin <ldv@strace.io>
Signed-off-by: Elvira Khabirova <lineprinter0@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>