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zram: avoid NULL pointer access in concurrent situation

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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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Weijie Yang 2014-10-29 14:50:57 -07:00 committed by Linus Torvalds
parent 8aba7e0a2c
commit 5a99e95b8d
1 changed files with 6 additions and 4 deletions
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10
drivers/block/zram/zram_drv.c
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@ -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;