kfence: Avoid stalling work queue task without allocations

kfence: Avoid stalling work queue task without allocations

To toggle the allocation gates, we set up a delayed work that calls
toggle_allocation_gate(). Here we use wait_event() to await an
allocation and subsequently disable the static branch again. However, if
the kernel has stopped doing allocations entirely, we'd wait
indefinitely, and stall the worker task. This may also result in the
appropriate warnings if CONFIG_DETECT_HUNG_TASK=y.

Therefore, introduce a 1 second timeout and use wait_event_timeout(). If
the timeout is reached, the static branch is disabled and a new delayed
work is scheduled to try setting up an allocation at a later time.

Note that, this scenario is very unlikely during normal workloads once
the kernel has booted and user space tasks are running. It can, however,
happen during early boot after KFENCE has been enabled, when e.g.
running tests that do not result in any allocations.

Link: https://lkml.kernel.org/r/CADYN=9J0DQhizAGB0-jz4HOBBh+05kMBXb4c0cXMS7Qi5NAJiw@mail.gmail.com
Reported-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Marco Elver <elver@google.com>
[port kfence feature to rpi-5.10.95]
Signed-off-by: Sung-hun Kim <sfoon.kim@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: Ia4e37404fce3497d6c9d32cae23ffa5d106055da