CVE-2019-19813: Use After Free

In the Linux kernel 5.0.21, mounting a crafted btrfs filesystem image, performing some operations, and then making a syncfs system call can lead to a use-after-free in mutexlock in kernel/locking/mutex.c. This is related to mutexcanspinonowner in kernel/locking/mutex.c, btrfsqgroupfreemeta in...