--- /dev/null
+From 5abbe51a526253b9f003e9a0a195638dc882d660 Mon Sep 17 00:00:00 2001
+From: Oleg Nesterov <oleg@redhat.com>
+Date: Mon, 1 Feb 2021 18:46:41 +0100
+Subject: kernel, fs: Introduce and use set_restart_fn() and arch_set_restart_data()
+
+From: Oleg Nesterov <oleg@redhat.com>
+
+commit 5abbe51a526253b9f003e9a0a195638dc882d660 upstream.
+
+Preparation for fixing get_nr_restart_syscall() on X86 for COMPAT.
+
+Add a new helper which sets restart_block->fn and calls a dummy
+arch_set_restart_data() helper.
+
+Fixes: 609c19a385c8 ("x86/ptrace: Stop setting TS_COMPAT in ptrace code")
+Signed-off-by: Oleg Nesterov <oleg@redhat.com>
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+Cc: stable@vger.kernel.org
+Link: https://lore.kernel.org/r/20210201174641.GA17871@redhat.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ fs/select.c | 10 ++++------
+ include/linux/thread_info.h | 13 +++++++++++++
+ kernel/futex.c | 3 +--
+ kernel/time/alarmtimer.c | 2 +-
+ kernel/time/hrtimer.c | 2 +-
+ kernel/time/posix-cpu-timers.c | 2 +-
+ 6 files changed, 21 insertions(+), 11 deletions(-)
+
+--- a/fs/select.c
++++ b/fs/select.c
+@@ -1006,10 +1006,9 @@ static long do_restart_poll(struct resta
+
+ ret = do_sys_poll(ufds, nfds, to);
+
+- if (ret == -EINTR) {
+- restart_block->fn = do_restart_poll;
+- ret = -ERESTART_RESTARTBLOCK;
+- }
++ if (ret == -EINTR)
++ ret = set_restart_fn(restart_block, do_restart_poll);
++
+ return ret;
+ }
+
+@@ -1031,7 +1030,6 @@ SYSCALL_DEFINE3(poll, struct pollfd __us
+ struct restart_block *restart_block;
+
+ restart_block = ¤t->restart_block;
+- restart_block->fn = do_restart_poll;
+ restart_block->poll.ufds = ufds;
+ restart_block->poll.nfds = nfds;
+
+@@ -1042,7 +1040,7 @@ SYSCALL_DEFINE3(poll, struct pollfd __us
+ } else
+ restart_block->poll.has_timeout = 0;
+
+- ret = -ERESTART_RESTARTBLOCK;
++ ret = set_restart_fn(restart_block, do_restart_poll);
+ }
+ return ret;
+ }
+--- a/include/linux/thread_info.h
++++ b/include/linux/thread_info.h
+@@ -11,6 +11,7 @@
+ #include <linux/types.h>
+ #include <linux/bug.h>
+ #include <linux/restart_block.h>
++#include <linux/errno.h>
+
+ #ifdef CONFIG_THREAD_INFO_IN_TASK
+ /*
+@@ -39,6 +40,18 @@ enum {
+
+ #ifdef __KERNEL__
+
++#ifndef arch_set_restart_data
++#define arch_set_restart_data(restart) do { } while (0)
++#endif
++
++static inline long set_restart_fn(struct restart_block *restart,
++ long (*fn)(struct restart_block *))
++{
++ restart->fn = fn;
++ arch_set_restart_data(restart);
++ return -ERESTART_RESTARTBLOCK;
++}
++
+ #ifndef THREAD_ALIGN
+ #define THREAD_ALIGN THREAD_SIZE
+ #endif
+--- a/kernel/futex.c
++++ b/kernel/futex.c
+@@ -2875,14 +2875,13 @@ retry:
+ goto out;
+
+ restart = ¤t->restart_block;
+- restart->fn = futex_wait_restart;
+ restart->futex.uaddr = uaddr;
+ restart->futex.val = val;
+ restart->futex.time = *abs_time;
+ restart->futex.bitset = bitset;
+ restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
+
+- ret = -ERESTART_RESTARTBLOCK;
++ ret = set_restart_fn(restart, futex_wait_restart);
+
+ out:
+ if (to) {
+--- a/kernel/time/alarmtimer.c
++++ b/kernel/time/alarmtimer.c
+@@ -822,9 +822,9 @@ static int alarm_timer_nsleep(const cloc
+ if (flags == TIMER_ABSTIME)
+ return -ERESTARTNOHAND;
+
+- restart->fn = alarm_timer_nsleep_restart;
+ restart->nanosleep.clockid = type;
+ restart->nanosleep.expires = exp;
++ set_restart_fn(restart, alarm_timer_nsleep_restart);
+ return ret;
+ }
+
+--- a/kernel/time/hrtimer.c
++++ b/kernel/time/hrtimer.c
+@@ -1545,9 +1545,9 @@ long hrtimer_nanosleep(const struct time
+ }
+
+ restart = ¤t->restart_block;
+- restart->fn = hrtimer_nanosleep_restart;
+ restart->nanosleep.clockid = t.timer.base->clockid;
+ restart->nanosleep.expires = hrtimer_get_expires_tv64(&t.timer);
++ set_restart_fn(restart, hrtimer_nanosleep_restart);
+ out:
+ destroy_hrtimer_on_stack(&t.timer);
+ return ret;
+--- a/kernel/time/posix-cpu-timers.c
++++ b/kernel/time/posix-cpu-timers.c
+@@ -1348,8 +1348,8 @@ static int posix_cpu_nsleep(const clocki
+ if (flags & TIMER_ABSTIME)
+ return -ERESTARTNOHAND;
+
+- restart_block->fn = posix_cpu_nsleep_restart;
+ restart_block->nanosleep.clockid = which_clock;
++ set_restart_fn(restart_block, posix_cpu_nsleep_restart);
+ }
+ return error;
+ }