Hi Stephen, On 06.08.2019 01:32, Stephen Boyd wrote: > The hwrng_fill() function can run while devices are suspending and > resuming. If the hwrng is behind a bus such as i2c or SPI and that bus > is suspended, the hwrng may hang the bus while attempting to add some > randomness. It's been observed on ChromeOS devices with suspend-to-idle > (s2idle) and an i2c based hwrng that this kthread may run and ask the > hwrng device for randomness before the i2c bus has been resumed. > > Let's make this kthread freezable so that we don't try to touch the > hwrng during suspend/resume. This ensures that we can't cause the hwrng > backing driver to get into a bad state because the device is guaranteed > to be resumed before the hwrng kthread is thawed. This patch broke suspend with virtio-rng loaded (it hangs). The problematic call chain is: virtrng_freeze() -> remove_common() -> hwrng_unregister() -> kthread_stop(). It looks like kthread_stop() can't finish on a frozen khwrng thread. Reverting this commit makes a VM with virtio-rng driver loaded suspend and resume correctly again. Maciej
