percpu: initialize best_upa variable

Tom reported this finding from clang 10's static analysis [1].

Due to the way the code is written, it will always see a successful loop
iteration. Instead of setting an initial value, check that it was set
instead with BUG_ON() because 0 units per allocation is bogus.

[1] https://lore.kernel.org/lkml/20210515180817.1751084-1-trix@redhat.com/

Reported-by: Tom Rix <trix@redhat.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>

diff --git a/mm/percpu.c b/mm/percpu.c
index e7b9ca82e9aa89f96620096165515751f71f170c..6667dfa0fcec16c4c181540bbd7136b9430cbd35 100644 (file)
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2888,6 +2888,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
         * Related to atom_size, which could be much larger than the unit_size.
         */
        last_allocs = INT_MAX;
+       best_upa = 0;
        for (upa = max_upa; upa; upa--) {
                int allocs = 0, wasted = 0;
 
@@ -2914,6 +2915,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
                last_allocs = allocs;
                best_upa = upa;
        }
+       BUG_ON(!best_upa);
        upa = best_upa;
 
        /* allocate and fill alloc_info */