perf: arm_spe: Make wakeup range check overflow safe

The current code checks whether the wakeup point is in the current
writable range by comparing it with handle->head + handle->size.

The perf AUX head is a monotonically increasing index, so that addition
can overflow when head is close to ULONG_MAX. In that case, a wakeup
point which is still inside the free space range can be missed.

Use unsigned subtraction to compare the distance from head to wakeup
against the handle->size. This can dismiss the issue when addition
overflow.

This is unlikely to happen in practice, but the change makes the
watermark check logically correct.

Fixes: d5d9696b0380 ("drivers/perf: Add support for ARMv8.2 Statistical Profiling Extension")
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

0 files changed, 0 insertions, 0 deletions