linux-kernel - [PATCH 02/16] lib/bitmap: don't call bitmap

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Date:   Mon, 18 Jul 2022 12:28:30 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Klimov <aklimov@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ben Segall <bsegall@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dennis Zhou <dennis@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Eric Dumazet <edumazet@...gle.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Ingo Molnar <mingo@...hat.com>,
        Isabella Basso <isabbasso@...eup.net>,
        John Fastabend <john.fastabend@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        KP Singh <kpsingh@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Mel Gorman <mgorman@...e.de>, Miroslav Benes <mbenes@...e.cz>,
        Nathan Chancellor <nathan@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tejun Heo <tj@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yonghong Song <yhs@...com>,
        Yury Norov <yury.norov@...il.com>, linux-mm@...ck.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH 02/16] lib/bitmap: don't call bitmap_set() with len == 0

bitmap_parselist() format allows passing 0-length regions, but because
len == 0 is not covered by small_const_nbits() macro, we have to call
__bitmap_set() and do some prologue calculations just for nothing.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 lib/bitmap.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index cd4dd848ea6a..790df2ea02df 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -712,10 +712,13 @@ struct region {
 
 static void bitmap_set_region(const struct region *r, unsigned long *bitmap)
 {
-	unsigned int start;
+	unsigned int start, len;
 
-	for (start = r->start; start <= r->end; start += r->group_len)
-		bitmap_set(bitmap, start, min(r->end - start + 1, r->off));
+	for (start = r->start; start <= r->end; start += r->group_len) {
+		len = min(r->end - start + 1, r->off);
+		if (len > 0)
+			bitmap_set(bitmap, start, len);
+	}
 }
 
 static int bitmap_check_region(const struct region *r)
-- 
2.34.1