[PATCH] PM / suspend: move userspace freeze before disk sync

[Sean Nyekjaer <sean@geanix.com>]

This fixes an issue where data remains unwritten before suspend.
UBI tried to write data, before the mtd device had been unsuspended.

Seen on an iMX6ULL board fitted with rawnand flash.

Before:
PM: suspend entry (deep)
Filesystems sync: 0.088 seconds
Freezing user space processes ... (elapsed 0.000 seconds) done.
OOM killer disabled.
Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
printk: Suspending console(s) (use no_console_suspend to debug)
PM: suspend devices took 0.030 seconds
Disabling non-boot CPUs ...
ubi0 error: ubi_io_write: error -16 while writing 4096 bytes to PEB 1762:94208, written 0 bytes

After:
PM: suspend entry (deep)
Freezing user space processes ... (elapsed 0.001 seconds) done.
OOM killer disabled.
Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
Filesystems sync: 0.060 seconds
printk: Suspending console(s) (use no_console_suspend to debug)
PM: suspend devices took 0.040 seconds
Disabling non-boot CPUs ...
PM: resume devices took 0.100 seconds

Signed-off-by: Sean Nyekjaer <sean@geanix.com>
---

Some explanation/discussion here:
http://lists.infradead.org/pipermail/linux-mtd/2021-July/087390.html

 kernel/power/suspend.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 87331565e505..4ee3fcbb0e7a 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -562,6 +562,12 @@ static int enter_state(suspend_state_t state)
 	if (state == PM_SUSPEND_TO_IDLE)
 		s2idle_begin();
 
+	pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
+	pm_suspend_clear_flags();
+	error = suspend_prepare(state);
+	if (error)
+		goto Unlock;
+
 #ifndef CONFIG_SUSPEND_SKIP_SYNC
 	trace_suspend_resume(TPS("sync_filesystems"), 0, true);
 	pr_info("Syncing filesystems ... ");
@@ -570,12 +576,6 @@ static int enter_state(suspend_state_t state)
 	trace_suspend_resume(TPS("sync_filesystems"), 0, false);
 #endif
 
-	pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
-	pm_suspend_clear_flags();
-	error = suspend_prepare(state);
-	if (error)
-		goto Unlock;
-
 	if (suspend_test(TEST_FREEZER))
 		goto Finish;
 
-- 
2.33.0