[PATCH] zram: avoid NULL pointer access in concurrent situation

There is a rare NULL pointer bug in mem_used_total_show() and
mem_used_max_store() in concurrent situation, like this:

zram is not initialized, process A is a mem_used_total reader which runs
periodically, while process B try to init zram.

	process A 				process B
access meta, get a NULL value
						init zram, done
init_done() is true
access meta->mem_pool, get a NULL pointer BUG

This patch fixes this issue.

Signed-off-by: Weijie Yang <weijie.yang@samsung.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)