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| author | Weijie Yang <weijie.yang@samsung.com> | 2014-10-30 00:50:57 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-10-30 02:33:15 +0300 |
| commit | 5a99e95b8d1cd47f6feddcdca6c71d22060df8a2 (patch) | |
| tree | 51384759dcfdc6e189139a5a58a5df7f6e16f56b | |
| parent | 8aba7e0a2c02355f9a7dec629635cb7093fe0508 (diff) | |
| download | linux-5a99e95b8d1cd47f6feddcdca6c71d22060df8a2.tar.xz | |
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | drivers/block/zram/zram_drv.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 0e63e8aa8279..2ad0b5bce44b 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); @@ -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; |