[PATCH-next RESEND v2] lib: parser: optimize match_NUMER apis to use local array

[PATCH-next RESEND v2] lib: parser: optimize match_NUMER apis to use local array

[Li Lingfeng]

Memory will be allocated to store substring_t in match_strdup(), which means
the caller of match_strdup() may need to be scheduled out to wait for reclaiming
memory.

Using local array to store substring_t to remove the restriction.

Link: https://lore.kernel.org/all/20221104023938.2346986-5-yukuai1@huaweicloud.com/
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
 lib/parser.c | 42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)

diff --git a/lib/parser.c b/lib/parser.c
index bcb23484100e..0d00f0adb063 100644
--- a/lib/parser.c
+++ b/lib/parser.c
@@ -11,6 +11,15 @@
 #include <linux/slab.h>
 #include <linux/string.h>
 
+/*
+ * max size needed by diffrent bases to express U64
+ * HEX: "0xFFFFFFFFFFFFFFFF" --> 18
+ * DEC: "18446744073709551615" --> 20
+ * OCT: "01777777777777777777777" --> 23
+ * pick the max one to define NUMBER_BUF_LEN
+ */
+#define NUMBER_BUF_LEN 24
+
 /**
  * match_one - Determines if a string matches a simple pattern
  * @s: the string to examine for presence of the pattern
@@ -129,14 +138,13 @@ EXPORT_SYMBOL(match_token);
 static int match_number(substring_t *s, int *result, int base)
 {
 	char *endp;
-	char *buf;
+	char buf[NUMBER_BUF_LEN];
 	int ret;
 	long val;
 
-	buf = match_strdup(s);
-	if (!buf)
-		return -ENOMEM;
-
+	if ((s->to - s->from) >= NUMBER_BUF_LEN)
+		return -ERANGE;
+	match_strlcpy(buf, s, NUMBER_BUF_LEN);
 	ret = 0;
 	val = simple_strtol(buf, &endp, base);
 	if (endp == buf)
@@ -145,7 +153,6 @@ static int match_number(substring_t *s, int *result, int base)
 		ret = -ERANGE;
 	else
 		*result = (int) val;
-	kfree(buf);
 	return ret;
 }
 
@@ -163,18 +170,16 @@ static int match_number(substring_t *s, int *result, int base)
  */
 static int match_u64int(substring_t *s, u64 *result, int base)
 {
-	char *buf;
+	char buf[NUMBER_BUF_LEN];
 	int ret;
 	u64 val;
 
-	buf = match_strdup(s);
-	if (!buf)
-		return -ENOMEM;
-
+	if ((s->to - s->from) >= NUMBER_BUF_LEN)
+		return -ERANGE;
+	match_strlcpy(buf, s, NUMBER_BUF_LEN);
 	ret = kstrtoull(buf, base, &val);
 	if (!ret)
 		*result = val;
-	kfree(buf);
 	return ret;
 }
 
@@ -206,14 +211,13 @@ EXPORT_SYMBOL(match_int);
  */
 int match_uint(substring_t *s, unsigned int *result)
 {
-	int err = -ENOMEM;
-	char *buf = match_strdup(s);
+	char buf[NUMBER_BUF_LEN];
 
-	if (buf) {
-		err = kstrtouint(buf, 10, result);
-		kfree(buf);
-	}
-	return err;
+	if ((s->to - s->from) >= NUMBER_BUF_LEN)
+		return -ERANGE;
+	match_strlcpy(buf, s, NUMBER_BUF_LEN);
+
+	return kstrtouint(buf, 10, result);
 }
 EXPORT_SYMBOL(match_uint);
 
-- 
2.31.1

Re: [PATCH v2] lib: parser: optimize match_NUMER apis to use local array

[Eric Biggers]

On Wed, Jan 11, 2023 at 12:22:15PM +0800, Li Lingfeng wrote:
>  /**
>   * match_one - Determines if a string matches a simple pattern
>   * @s: the string to examine for presence of the pattern
> @@ -129,14 +138,13 @@ EXPORT_SYMBOL(match_token);
>  static int match_number(substring_t *s, int *result, int base)
>  {
>  	char *endp;
> -	char *buf;
> +	char buf[NUMBER_BUF_LEN];
>  	int ret;
>  	long val;
>  
> -	buf = match_strdup(s);
> -	if (!buf)
> -		return -ENOMEM;
> -
> +	if ((s->to - s->from) >= NUMBER_BUF_LEN)
> +		return -ERANGE;
> +	match_strlcpy(buf, s, NUMBER_BUF_LEN);

Instead of doing '(s->to - s->from) >= NUMBER_BUF_LEN', it would be simpler to
check the return value of match_strlcpy():

	if (match_strlcpy(buf, s, NUMBER_BUF_LEN) >= NUMBER_BUF_LEN)
		return -ERANGE;

Likewise in match_u64int() and match_uint().

- Eric

Re: [PATCH-next RESEND v2] lib: parser: optimize match_NUMER apis to use local array

[Tejun Heo]

On Wed, Jan 11, 2023 at 12:22:15PM +0800, Li Lingfeng wrote:
> Memory will be allocated to store substring_t in match_strdup(), which means
> the caller of match_strdup() may need to be scheduled out to wait for reclaiming
> memory.
> 
> Using local array to store substring_t to remove the restriction.
> 
> Link: https://lore.kernel.org/all/20221104023938.2346986-5-yukuai1@huaweicloud.com/
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
> Acked-by: Tejun Heo <tj@kernel.org>

This will fix a sleep-in-atomic in #linus, so it'd be great if we can get it
merged. Can you please apply the suggested changes and repost? I think we
can route this through block too as the current breakage is there. So,
please cc Jens too.

Thanks.

-- 
tejun