linux-kernel - [PATCH 1/1] percpu: initialize best

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Date:   Mon, 14 Jun 2021 14:50:49 +0000
From:   Dennis Zhou <dennis@...nel.org>
To:     Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Dennis Zhou <dennis@...nel.org>, Tom Rix <trix@...hat.com>
Subject: [PATCH 1/1] 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@...hat.com>
Signed-off-by: Dennis Zhou <dennis@...nel.org>
---
Sorry this hasn't been my highest priority. I'll apply this shortly to
for-5.14.

 mm/percpu.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/percpu.c b/mm/percpu.c
index e7b9ca82e9aa..6667dfa0fcec 100644
--- 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 */
-- 
2.32.0.272.g935e593368-goog