On Mon, Oct 14, 2019 at 05:53:59PM +0800, Chen Wandun wrote:

From: Chenwandun chenwandun@huawei.com

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);

get the value of zram->backing_dev too early in backing_dev_show, that will result the value may be NULL at the begining, 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

Signed-off-by: Chenwandun chenwandun@huawei.com

It should be stable material. Cc: stable@vger.kernel.org [4.14+] Acked-by: Minchan Kim minchan@kernel.org

Thanks!