diff mbox

[9/10] drivers/mmc: Move a dereference below a NULL test

Message ID Pine.LNX.4.64.0907191729580.16542@ask.diku.dk (mailing list archive)
State Awaiting Upstream, archived
Headers show

Commit Message

Julia Lawall July 19, 2009, 3:30 p.m. UTC 
From: Julia Lawall <julia@diku.dk>

If the NULL test is necessary, then the dereference should be moved below
the NULL test.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
type T;
expression E,E1;
identifier i,fld;
statement S;
@@

- T i = E->fld;
+ T i;
  ... when != E=E1
      when != i
  BUG_ON (E == NULL||
-     i
+     E->fld
       == NULL || ...);
+ i = E->fld;
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>

---
 drivers/mmc/host/omap.c             |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

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Comments

Adrian Hunter July 20, 2009, 8:01 a.m. UTC | #1 
Julia Lawall wrote:
> From: Julia Lawall <julia@diku.dk>
> 
> If the NULL test is necessary, then the dereference should be moved below
> the NULL test.
> 
> The semantic patch that makes this change is as follows:
> (http://www.emn.fr/x-info/coccinelle/)
> 
> // <smpl>
> @@
> type T;
> expression E,E1;
> identifier i,fld;
> statement S;
> @@
> 
> - T i = E->fld;
> + T i;
>   ... when != E=E1
>       when != i
>   BUG_ON (E == NULL||
> -     i
> +     E->fld
>        == NULL || ...);
> + i = E->fld;
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@diku.dk>
> 
> ---
>  drivers/mmc/host/omap.c             |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
> index e7a331d..89281ab 100644
> --- a/drivers/mmc/host/omap.c
> +++ b/drivers/mmc/host/omap.c
> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct work_struct *work)
>  
>  static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
>  {
> -	struct mmc_omap_host *host = slot->host;
> +	struct mmc_omap_host *host;
>  	unsigned long flags;
>  	int i;
>  
> -	BUG_ON(slot == NULL || host->mmc == NULL);
> +	BUG_ON(slot == NULL || slot->host->mmc == NULL);
> +	host = slot->host;
>  
>  	if (clk_enabled)
>  		/* Keeps clock running for at least 8 cycles on valid freq */
> --

If slot is NULL it will oops anyway, so the following is better IMHO:
 
static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
{
	struct mmc_omap_host *host = slot->host;
	unsigned long flags;
	int i;

> -	BUG_ON(slot == NULL || host->mmc == NULL);
> +	BUG_ON(host->mmc == NULL);

	if (clk_enabled)
		/* Keeps clock running for at least 8 cycles on valid freq */
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arun c July 20, 2009, 12:33 p.m. UTC | #2 
On Mon, Jul 20, 2009 at 1:31 PM, Adrian Hunter<adrian.hunter@nokia.com> wrote:
> Julia Lawall wrote:
>>
>> From: Julia Lawall <julia@diku.dk>
>>
>> If the NULL test is necessary, then the dereference should be moved below
>> the NULL test.
>>
>> The semantic patch that makes this change is as follows:
>> (http://www.emn.fr/x-info/coccinelle/)
>>
>> // <smpl>
>> @@
>> type T;
>> expression E,E1;
>> identifier i,fld;
>> statement S;
>> @@
>>
>> - T i = E->fld;
>> + T i;
>>  ... when != E=E1
>>      when != i
>>  BUG_ON (E == NULL||
>> -     i
>> +     E->fld
>>       == NULL || ...);
>> + i = E->fld;
>> // </smpl>
>>
>> Signed-off-by: Julia Lawall <julia@diku.dk>
>>
>> ---
>>  drivers/mmc/host/omap.c             |    5 +++--
>>  1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
>> index e7a331d..89281ab 100644
>> --- a/drivers/mmc/host/omap.c
>> +++ b/drivers/mmc/host/omap.c
>> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct
>> work_struct *work)
>>   static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
>> clk_enabled)
>>  {
>> -       struct mmc_omap_host *host = slot->host;
>> +       struct mmc_omap_host *host;
>>        unsigned long flags;
>>        int i;
>>  -       BUG_ON(slot == NULL || host->mmc == NULL);
>> +       BUG_ON(slot == NULL || slot->host->mmc == NULL);
>> +       host = slot->host;
>>          if (clk_enabled)
>>                /* Keeps clock running for at least 8 cycles on valid freq
>> */
>> --
>
> If slot is NULL it will oops anyway, so the following is better IMHO:
>
> static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
> clk_enabled)
> {
>        struct mmc_omap_host *host = slot->host;
>        unsigned long flags;
>        int i;
>
>> -       BUG_ON(slot == NULL || host->mmc == NULL);
>> +       BUG_ON(host->mmc == NULL);
>
>        if (clk_enabled)
>                /* Keeps clock running for at least 8 cycles on valid freq */
> --

According to http://isc.sans.org/diary.html?storyid=6820&rss "NULL check"
must be done before assigning the values. Does Julia Lawall's version
is the more correct one??

Arun
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Adrian Hunter July 20, 2009, 12:43 p.m. UTC | #3 
arun c wrote:
> On Mon, Jul 20, 2009 at 1:31 PM, Adrian Hunter<adrian.hunter@nokia.com> wrote:
>> Julia Lawall wrote:
>>> From: Julia Lawall <julia@diku.dk>
>>>
>>> If the NULL test is necessary, then the dereference should be moved below
>>> the NULL test.
>>>
>>> The semantic patch that makes this change is as follows:
>>> (http://www.emn.fr/x-info/coccinelle/)
>>>
>>> // <smpl>
>>> @@
>>> type T;
>>> expression E,E1;
>>> identifier i,fld;
>>> statement S;
>>> @@
>>>
>>> - T i = E->fld;
>>> + T i;
>>>  ... when != E=E1
>>>      when != i
>>>  BUG_ON (E == NULL||
>>> -     i
>>> +     E->fld
>>>       == NULL || ...);
>>> + i = E->fld;
>>> // </smpl>
>>>
>>> Signed-off-by: Julia Lawall <julia@diku.dk>
>>>
>>> ---
>>>  drivers/mmc/host/omap.c             |    5 +++--
>>>  1 files changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
>>> index e7a331d..89281ab 100644
>>> --- a/drivers/mmc/host/omap.c
>>> +++ b/drivers/mmc/host/omap.c
>>> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct
>>> work_struct *work)
>>>   static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
>>> clk_enabled)
>>>  {
>>> -       struct mmc_omap_host *host = slot->host;
>>> +       struct mmc_omap_host *host;
>>>        unsigned long flags;
>>>        int i;
>>>  -       BUG_ON(slot == NULL || host->mmc == NULL);
>>> +       BUG_ON(slot == NULL || slot->host->mmc == NULL);
>>> +       host = slot->host;
>>>          if (clk_enabled)
>>>                /* Keeps clock running for at least 8 cycles on valid freq
>>> */
>>> --
>> If slot is NULL it will oops anyway, so the following is better IMHO:
>>
>> static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int
>> clk_enabled)
>> {
>>        struct mmc_omap_host *host = slot->host;
>>        unsigned long flags;
>>        int i;
>>
>>> -       BUG_ON(slot == NULL || host->mmc == NULL);
>>> +       BUG_ON(host->mmc == NULL);
>>        if (clk_enabled)
>>                /* Keeps clock running for at least 8 cycles on valid freq */
>> --
> 
> According to http://isc.sans.org/diary.html?storyid=6820&rss "NULL check"
> must be done before assigning the values. Does Julia Lawall's version
> is the more correct one??
> 
> Arun

It is not a "NULL check" it is an assertion, which can be compiled out.
On some platforms BUG is implemented as a null dereference anyway
e.g. on ARM  it is *(int *)0 = 0;

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Alan Cox July 20, 2009, 12:47 p.m. UTC | #4 
> It is not a "NULL check" it is an assertion, which can be compiled out.
> On some platforms BUG is implemented as a null dereference anyway
> e.g. on ARM  it is *(int *)0 = 0;

It's a bogus check because the 

struct mmc_omap_host *host = slot->host;

has already been executed before you check for slot == NULL

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diff mbox

Patch

diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
index e7a331d..89281ab 100644
--- a/drivers/mmc/host/omap.c
+++ b/drivers/mmc/host/omap.c
@@ -255,11 +255,12 @@  static void mmc_omap_slot_release_work(struct work_struct *work)
 
 static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
 {
-	struct mmc_omap_host *host = slot->host;
+	struct mmc_omap_host *host;
 	unsigned long flags;
 	int i;
 
-	BUG_ON(slot == NULL || host->mmc == NULL);
+	BUG_ON(slot == NULL || slot->host->mmc == NULL);
+	host = slot->host;
 
 	if (clk_enabled)
 		/* Keeps clock running for at least 8 cycles on valid freq */