[PATCH] char/misc.c: misc_register: Do not loop on misc_list unconditionally

[PATCH] char/misc.c: misc_register: Do not loop on misc_list unconditionally

[Dae S. Kim]

If the minor number is assigned dynamically, there is no need to
search for misc->minor in misc_list, since misc->minor == 
MISC_DYNAMIC_MINOR.

Signed-off-by: Dae S. Kim <dae@velatum.com>
---
 drivers/char/misc.c |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index 522136d..7b262b6 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -190,12 +190,6 @@ int misc_register(struct miscdevice * misc)
 	INIT_LIST_HEAD(&misc->list);
 
 	mutex_lock(&misc_mtx);
-	list_for_each_entry(c, &misc_list, list) {
-		if (c->minor == misc->minor) {
-			mutex_unlock(&misc_mtx);
-			return -EBUSY;
-		}
-	}
 
 	if (misc->minor == MISC_DYNAMIC_MINOR) {
 		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
@@ -205,6 +199,13 @@ int misc_register(struct miscdevice * misc)
 		}
 		misc->minor = DYNAMIC_MINORS - i - 1;
 		set_bit(i, misc_minors);
+	} else {
+		list_for_each_entry(c, &misc_list, list) {
+			if (c->minor == misc->minor) {
+				mutex_unlock(&misc_mtx);
+				return -EBUSY;
+			}
+		}
 	}
 
 	dev = MKDEV(MISC_MAJOR, misc->minor);
-- 
1.7.9.5

Re: [PATCH] char/misc.c: misc_register: Do not loop on misc_list unconditionally

[Andrew Morton]

On Mon, 17 Dec 2012 23:26:38 +0100
"Dae S. Kim" <dae@velatum.com> wrote:

> If the minor number is assigned dynamically, there is no need to
> search for misc->minor in misc_list, since misc->minor == 
> MISC_DYNAMIC_MINOR.
> 
> ...
>
> --- a/drivers/char/misc.c
> +++ b/drivers/char/misc.c
> @@ -190,12 +190,6 @@ int misc_register(struct miscdevice * misc)
>  	INIT_LIST_HEAD(&misc->list);
>  
>  	mutex_lock(&misc_mtx);
> -	list_for_each_entry(c, &misc_list, list) {
> -		if (c->minor == misc->minor) {
> -			mutex_unlock(&misc_mtx);
> -			return -EBUSY;
> -		}
> -	}
>  
>  	if (misc->minor == MISC_DYNAMIC_MINOR) {
>  		int i = find_first_zero_bit(misc_minors, DYNAMIC_MINORS);
> @@ -205,6 +199,13 @@ int misc_register(struct miscdevice * misc)
>  		}
>  		misc->minor = DYNAMIC_MINORS - i - 1;
>  		set_bit(i, misc_minors);
> +	} else {
> +		list_for_each_entry(c, &misc_list, list) {
> +			if (c->minor == misc->minor) {
> +				mutex_unlock(&misc_mtx);
> +				return -EBUSY;
> +			}
> +		}
>  	}
>  

Looks OK.  It permits this:



From: Andrew Morton <akpm@linux-foundation.org>
Subject: drivers-char-miscc-misc_register-do-not-loop-on-misc_list-unconditionally-fix

reduce scope of local `c'

Cc: "Dae S. Kim" <dae@velatum.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dae S. Kim <dae@velatum.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 drivers/char/misc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff -puN drivers/char/misc.c~drivers-char-miscc-misc_register-do-not-loop-on-misc_list-unconditionally-fix drivers/char/misc.c
--- a/drivers/char/misc.c~drivers-char-miscc-misc_register-do-not-loop-on-misc_list-unconditionally-fix
+++ a/drivers/char/misc.c
@@ -183,7 +183,6 @@ static const struct file_operations misc
  
 int misc_register(struct miscdevice * misc)
 {
-	struct miscdevice *c;
 	dev_t dev;
 	int err = 0;
 
@@ -200,6 +199,8 @@ int misc_register(struct miscdevice * mi
 		misc->minor = DYNAMIC_MINORS - i - 1;
 		set_bit(i, misc_minors);
 	} else {
+		struct miscdevice *c;
+
 		list_for_each_entry(c, &misc_list, list) {
 			if (c->minor == misc->minor) {
 				mutex_unlock(&misc_mtx);
_