Messages in this thread Patch in this message | | | From | Weijie Yang <> | Subject | [PATCH 2/2] zram: avoid NULL pointer access when reading mem_used_total | Date | Sat, 25 Oct 2014 17:26:31 +0800 |
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There is a rare NULL pointer bug in mem_used_total_show() in concurrent situation, like this: zram is not initialized, process A is a mem_used_total reader which runs periodicity, 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> --- drivers/block/zram/zram_drv.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 64dd79a..2ffd7d8 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -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); -- 1.7.0.4
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