From: Chenwandun <chenwandun@xxxxxxxxxx>
Subject: zram: fix race between backing_dev_show and backing_dev_store
CPU0: CPU1:
backing_dev_show backing_dev_store
...... ......
file = zram->backing_dev;
down_read(&zram->init_lock); down_read(&zram->init_init_lock)
file_path(file, ...); zram->backing_dev = backing_dev;
up_read(&zram->init_lock); up_read(&zram->init_lock);
gets the value of zram->backing_dev too early in backing_dev_show, which
resultin the value being NULL at the beginning, and not NULL later.
backtrace:
[<ffffff8570e0f3ec>] d_path+0xcc/0x174
[<ffffff8570decd90>] file_path+0x10/0x18
[<ffffff85712f7630>] backing_dev_show+0x40/0xb4
[<ffffff85712c776c>] dev_attr_show+0x20/0x54
[<ffffff8570e835e4>] sysfs_kf_seq_show+0x9c/0x10c
[<ffffff8570e82b98>] kernfs_seq_show+0x28/0x30
[<ffffff8570e1c580>] seq_read+0x184/0x488
[<ffffff8570e81ec4>] kernfs_fop_read+0x5c/0x1a4
[<ffffff8570dee0fc>] __vfs_read+0x44/0x128
[<ffffff8570dee310>] vfs_read+0xa0/0x138
[<ffffff8570dee860>] SyS_read+0x54/0xb4
Link: http://lkml.kernel.org/r/1571046839-16814-1-git-send-email-chenwandun@xxxxxxxxxx
Signed-off-by: Chenwandun <chenwandun@xxxxxxxxxx>
Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.14+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/block/zram/zram_drv.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/drivers/block/zram/zram_drv.c~zram-fix-race-between-backing_dev_show-and-backing_dev_store
+++ a/drivers/block/zram/zram_drv.c
@@ -413,13 +413,14 @@ static void reset_bdev(struct zram *zram
static ssize_t backing_dev_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
+ struct file *file;
struct zram *zram = dev_to_zram(dev);
- struct file *file = zram->backing_dev;
char *p;
ssize_t ret;
down_read(&zram->init_lock);
- if (!zram->backing_dev) {
+ file = zram->backing_dev;
+ if (!file) {
memcpy(buf, "none\n", 5);
up_read(&zram->init_lock);
return 5;
_
