The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f7daefe4231e57381d92c2e2ad905a899c28e402 Mon Sep 17 00:00:00 2001

From: Chenwandun chenwandun@huawei.com Date: Fri, 18 Oct 2019 20:20:14 -0700 Subject: [PATCH] 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: d_path+0xcc/0x174 file_path+0x10/0x18 backing_dev_show+0x40/0xb4 dev_attr_show+0x20/0x54 sysfs_kf_seq_show+0x9c/0x10c kernfs_seq_show+0x28/0x30 seq_read+0x184/0x488 kernfs_fop_read+0x5c/0x1a4 __vfs_read+0x44/0x128 vfs_read+0xa0/0x138 SyS_read+0x54/0xb4

Link: http://lkml.kernel.org/r/1571046839-16814-1-git-send-email-chenwandun@huawei... Signed-off-by: Chenwandun chenwandun@huawei.com Acked-by: Minchan Kim minchan@kernel.org Cc: Sergey Senozhatsky sergey.senozhatsky.work@gmail.com Cc: Jens Axboe axboe@kernel.dk Cc: stable@vger.kernel.org [4.14+] Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index d58a359a6622..4285e75e52c3 100644 --- a/drivers/block/zram/zram_drv.c +++ b/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;