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Commit 5a99e95b authored by Weijie Yang's avatar Weijie Yang Committed by Linus Torvalds
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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: default avatarWeijie Yang <weijie.yang@samsung.com>
Acked-by: default avatarMinchan Kim <minchan@kernel.org>
Acked-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8aba7e0a

drivers/block/zram/zram_drv.c

+6 −4
Original line number Diff line number Diff line
@@ -99,11 +99,12 @@ static ssize_t mem_used_total_show(struct device *dev, 
{

	u64 val = 0;

	struct zram *zram = dev_to_zram(dev);

	struct zram_meta *meta = zram->meta;



	down_read(&zram->init_lock);

	if (init_done(zram))

	if (init_done(zram)) {

		struct zram_meta *meta = zram->meta;

		val = zs_get_total_pages(meta->mem_pool);

	}

	up_read(&zram->init_lock);



	return scnprintf(buf, PAGE_SIZE, "%llu\n", val << PAGE_SHIFT);
@@ -173,16 +174,17 @@ static ssize_t mem_used_max_store(struct device *dev, 
	int err;

	unsigned long val;

	struct zram *zram = dev_to_zram(dev);

	struct zram_meta *meta = zram->meta;



	err = kstrtoul(buf, 10, &val);

	if (err || val != 0)

		return -EINVAL;



	down_read(&zram->init_lock);

	if (init_done(zram))

	if (init_done(zram)) {

		struct zram_meta *meta = zram->meta;

		atomic_long_set(&zram->stats.max_used_pages,

				zs_get_total_pages(meta->mem_pool));

	}

	up_read(&zram->init_lock);



	return len;