lib: dhry: fix unstable smp_processor_id(_) usage

When running the in-kernel Dhrystone benchmark with
CONFIG_DEBUG_PREEMPT=y:

    BUG: using smp_processor_id() in preemptible [00000000] code: bash/938

Fix this by not using smp_processor_id() directly, but instead wrapping
the whole benchmark inside a get_cpu()/put_cpu() pair.  This makes sure
the whole benchmark is run on the same CPU core, and the reported values
are consistent.

Link: https://lkml.kernel.org/r/b0d29932bb24ad82cea7f821e295c898e9657be0.1678890070.git.geert+renesas@glider.be
Fixes: d5528cc16893f1f6 ("lib: add Dhrystone benchmark test")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reported-by: Tobias Klausmann <klausman@schwarzvogel.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217179
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/dhry_run.c b/lib/dhry_run.c
index f9d33ef..f15ac66 100644 (file)
--- a/lib/dhry_run.c
+++ b/lib/dhry_run.c
@@ -31,6 +31,7 @@ MODULE_PARM_DESC(iterations,
 
 static void dhry_benchmark(void)
 {
+       unsigned int cpu = get_cpu();
        int i, n;
 
        if (iterations > 0) {
@@ -45,9 +46,10 @@ static void dhry_benchmark(void)
        }
 
 report:
+       put_cpu();
        if (n >= 0)
-               pr_info("CPU%u: Dhrystones per Second: %d (%d DMIPS)\n",
-                       smp_processor_id(), n, n / DHRY_VAX);
+               pr_info("CPU%u: Dhrystones per Second: %d (%d DMIPS)\n", cpu,
+                       n, n / DHRY_VAX);
        else if (n == -EAGAIN)
                pr_err("Please increase the number of iterations\n");
        else