refscale: Bounds-check module parameters

The default value for refscale.nreaders is -1, which results in the code
setting the value to three-quarters of the number of CPUs.  On single-CPU
systems, this results in three-quarters of the value one, which the C
language's integer arithmetic rounds to zero.  This in turn results in
a divide-by-zero error.

This commit therefore adds bounds checking to the refscale module
parameters, so that if they are less than one, they are set to the
value one.

Reported-by: kernel test robot <lkp@intel.com>
Tested-by "Chen, Rong A" <rong.a.chen@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 952595c678b37299a111e288cb8d4e711759dd14..fb5f20d9486a898a8f6bdcdba48c75380f69764d 100644 (file)
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -681,6 +681,12 @@ ref_scale_init(void)
        // Reader tasks (default to ~75% of online CPUs).
        if (nreaders < 0)
                nreaders = (num_online_cpus() >> 1) + (num_online_cpus() >> 2);
+       if (WARN_ONCE(loops <= 0, "%s: loops = %ld, adjusted to 1\n", __func__, loops))
+               loops = 1;
+       if (WARN_ONCE(nreaders <= 0, "%s: nreaders = %d, adjusted to 1\n", __func__, nreaders))
+               nreaders = 1;
+       if (WARN_ONCE(nruns <= 0, "%s: nruns = %d, adjusted to 1\n", __func__, nruns))
+               nruns = 1;
        reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        if (!reader_tasks) {