xen: privcmd: Switch from mutex to spinlock for irqfds

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: xen: privcmd: Switch from mutex to spinlock for irqfds irqfd_wakeup() gets EPOLLHUP, when it is called by eventfd_release() by way of wake_up_poll(&ctx->wqh, EPOLLHUP), which gets called under spin_lock_irqsave(). We can't use a mutex here as it will lead to a deadlock. Fix it by switching over to a spin lock.

References

• https://git.kernel.org/stable/c/c2775ae4d9227729f8ca9ee2a068f62a00d5ea9c
• https://git.kernel.org/stable/c/49f2a5da6785b2dbde93e291cae037662440346e
• https://git.kernel.org/stable/c/1c682593096a487fd9aebc079a307ff7a6d054a3