rcu: fix shrink budget underflow in lazy_rcu_shrink_scan

The lazy RCU shrinker decremented sc->nr_to_scan (unsigned long)
and then tested the result with <= 0.  When a single CPU's lazy
callback count exceeds the remaining budget, the subtraction wraps
to a large positive value and the <= 0 comparison, which is
equivalent to == 0 for an unsigned type, never fires again.  The
scan loop then iterates through every nocb CPU instead of honouring
the reclaim budget.

Accumulate into count and stop once count >= nr_to_scan.

Fixes: c945b4da7a448 ("rcu: Shrinker for lazy rcu")
Assisted-by: Zcode:GLM-5.2
Signed-off-by: Longlong Xia <xialonglong@kylinos.cn>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

0 files changed, 0 insertions, 0 deletions