zram: clear IDLE flag in mark_idle()

If entry does not fulfill current mark_idle() parameters, e.g.  cutoff
time, then we should clear its ZRAM_IDLE from previous mark_idle()
invocations.

Consider the following case:
- mark_idle() cutoff time 8h
- mark_idle() cutoff time 4h
- writeback() idle - will writeback entries with cutoff time 8h,
  while it should only pick entries with cutoff time 4h

The bug was reported by Shin Kawamura.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 755804d ("zram: introduce an aged idle interface")
Signed-off-by: Sergey Senozhatsky <[email protected]>
Reported-by: Shin Kawamura <[email protected]>
Acked-by: Brian Geffon <[email protected]>
Cc: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: <[email protected]>

Author: sergey-senozhatsky

drivers/block/zram/zram_drv.c

@@ -410,6 +410,8 @@ static void mark_idle(struct zram *zram, ktime_t cutoff)
 #endif
 		if (is_idle)
 			zram_set_flag(zram, index, ZRAM_IDLE);
+		else
+			zram_clear_flag(zram, index, ZRAM_IDLE);
 		zram_slot_unlock(zram, index);
 	}
 }