kunit: irq: Ensure timer doesn't fire too frequently

kunit: irq: Ensure timer doesn't fire too frequently

Fix a bug where kunit_run_irq_test() could hang if the system is too
slow.  This was noticed with the crypto library tests in certain VMs.

Specifically, if kunit_irq_test_timer_func() and the associated hrtimer
code took over 5us to run, then the CPU would spend all its time
executing that code in hardirq context.  As a result, the task executing
kunit_run_irq_test() never had a chance to run, exit the loop, and
cancel the timer.

To fix it, make kunit_irq_test_timer_func() increase the timer interval
when the other contexts aren't having a chance to run.

Fixes: 950a81224e8b ("lib/crypto: tests: Add hash-test-template.h and gen-hash-testvecs.py")
Cc: stable@vger.kernel.org
Reviewed-by: David Gow <david@davidgow.net>
Link: https://lore.kernel.org/r/20260224033751.97615-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>