[PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Denis Efremov]

IS_ERR(), IS_ERR_OR_NULL(), IS_ERR_VALUE() and WARN*() already contain
unlikely() optimization internally. Thus, there is no point in calling
these functions and defines under likely()/unlikely().

This check is based on the coccinelle rule developed by Enrico Weigelt
https://lore.kernel.org/lkml/1559767582-11081-1-git-send-email-info@metux.net/

Signed-off-by: Denis Efremov <efremov@linux.com>
Cc: Joe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Whitcroft <apw@canonical.com>
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 93a7edfe0f05..56969ce06df4 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6480,6 +6480,12 @@ sub process {
 			     "Using $1 should generally have parentheses around the comparison\n" . $herecurr);
 		}
 
+# nested likely/unlikely calls
+		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
+			WARN("LIKELY_MISUSE",
+			     "nested (un)?likely() calls, $1 already uses unlikely() internally\n" . $herecurr);
+		}
+
 # whine mightly about in_atomic
 		if ($line =~ /\bin_atomic\s*\(/) {
 			if ($realfile =~ m@^drivers/@) {
-- 
2.21.0

[PATCH v3 02/11] drm/msm: remove unlikely() from WARN_ON() conditions

[Denis Efremov]

"unlikely(WARN_ON(x))" is excessive. WARN_ON() already uses unlikely()
internally.

Signed-off-by: Denis Efremov <efremov@linux.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Joe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
---
 drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c | 4 ++--
 drivers/gpu/drm/msm/disp/mdp_format.c    | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
index 4804cf40de14..030279d7b64b 100644
--- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
+++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
@@ -253,7 +253,7 @@ int mdp5_ctl_set_cursor(struct mdp5_ctl *ctl, struct mdp5_pipeline *pipeline,
 	u32 blend_cfg;
 	struct mdp5_hw_mixer *mixer = pipeline->mixer;
 
-	if (unlikely(WARN_ON(!mixer))) {
+	if (WARN_ON(!mixer)) {
 		DRM_DEV_ERROR(ctl_mgr->dev->dev, "CTL %d cannot find LM",
 			ctl->id);
 		return -EINVAL;
@@ -695,7 +695,7 @@ struct mdp5_ctl_manager *mdp5_ctlm_init(struct drm_device *dev,
 		goto fail;
 	}
 
-	if (unlikely(WARN_ON(ctl_cfg->count > MAX_CTL))) {
+	if (WARN_ON(ctl_cfg->count > MAX_CTL)) {
 		DRM_DEV_ERROR(dev->dev, "Increase static pool size to at least %d\n",
 				ctl_cfg->count);
 		ret = -ENOSPC;
diff --git a/drivers/gpu/drm/msm/disp/mdp_format.c b/drivers/gpu/drm/msm/disp/mdp_format.c
index 8afb0f9c04bb..5495d8b3f5b9 100644
--- a/drivers/gpu/drm/msm/disp/mdp_format.c
+++ b/drivers/gpu/drm/msm/disp/mdp_format.c
@@ -174,7 +174,7 @@ const struct msm_format *mdp_get_format(struct msm_kms *kms, uint32_t format,
 
 struct csc_cfg *mdp_get_default_csc_cfg(enum csc_type type)
 {
-	if (unlikely(WARN_ON(type >= CSC_MAX)))
+	if (WARN_ON(type >= CSC_MAX))
 		return NULL;
 
 	return &csc_convert[type];
-- 
2.21.0

Re: [PATCH v3 02/11] drm/msm: remove unlikely() from WARN_ON() conditions

[Bjorn Andersson]

On Thu 29 Aug 09:50 PDT 2019, Denis Efremov wrote:

> "unlikely(WARN_ON(x))" is excessive. WARN_ON() already uses unlikely()
> internally.
> 
> Signed-off-by: Denis Efremov <efremov@linux.com>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Sean Paul <sean@poorly.run>
> Cc: Joe Perches <joe@perches.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: linux-arm-msm@vger.kernel.org
> Cc: dri-devel@lists.freedesktop.org

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

> ---
>  drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c | 4 ++--
>  drivers/gpu/drm/msm/disp/mdp_format.c    | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c b/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
> index 4804cf40de14..030279d7b64b 100644
> --- a/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
> +++ b/drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c
> @@ -253,7 +253,7 @@ int mdp5_ctl_set_cursor(struct mdp5_ctl *ctl, struct mdp5_pipeline *pipeline,
>  	u32 blend_cfg;
>  	struct mdp5_hw_mixer *mixer = pipeline->mixer;
>  
> -	if (unlikely(WARN_ON(!mixer))) {
> +	if (WARN_ON(!mixer)) {
>  		DRM_DEV_ERROR(ctl_mgr->dev->dev, "CTL %d cannot find LM",
>  			ctl->id);
>  		return -EINVAL;
> @@ -695,7 +695,7 @@ struct mdp5_ctl_manager *mdp5_ctlm_init(struct drm_device *dev,
>  		goto fail;
>  	}
>  
> -	if (unlikely(WARN_ON(ctl_cfg->count > MAX_CTL))) {
> +	if (WARN_ON(ctl_cfg->count > MAX_CTL)) {
>  		DRM_DEV_ERROR(dev->dev, "Increase static pool size to at least %d\n",
>  				ctl_cfg->count);
>  		ret = -ENOSPC;
> diff --git a/drivers/gpu/drm/msm/disp/mdp_format.c b/drivers/gpu/drm/msm/disp/mdp_format.c
> index 8afb0f9c04bb..5495d8b3f5b9 100644
> --- a/drivers/gpu/drm/msm/disp/mdp_format.c
> +++ b/drivers/gpu/drm/msm/disp/mdp_format.c
> @@ -174,7 +174,7 @@ const struct msm_format *mdp_get_format(struct msm_kms *kms, uint32_t format,
>  
>  struct csc_cfg *mdp_get_default_csc_cfg(enum csc_type type)
>  {
> -	if (unlikely(WARN_ON(type >= CSC_MAX)))
> +	if (WARN_ON(type >= CSC_MAX))
>  		return NULL;
>  
>  	return &csc_convert[type];
> -- 
> 2.21.0
> 

Re: [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Markus Elfring]

> +# nested likely/unlikely calls
> +		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
> +			WARN("LIKELY_MISUSE",

How do you think about to use the specification “(?:IS_ERR(?:_(?:OR_NULL|VALUE))?|WARN)”
in this regular expression?

Regards,
Markus

Re: [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Denis Efremov]

On 31.08.2019 12:15, Markus Elfring wrote:
>> +# nested likely/unlikely calls
>> +        if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>> +            WARN("LIKELY_MISUSE",
> 
> How do you think about to use the specification “(?:IS_ERR(?:_(?:OR_NULL|VALUE))?|WARN)”
> in this regular expression?

Hmm, 
(?:   <- Catch group is required here, since it is used in diagnostic message,
         see $1
   IS_ERR
   (?:_ <- Another atomic group just to show that '_' is a common prefix?
           I'm not sure about this. Usually, Perl interpreter is very good at optimizing such things.
           You could see this optimization if you run perl with -Mre=debug.
     (?:OR_NULL|VALUE))?|WARN)

Regards,
Denis

Re: [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Markus Elfring]

>>> +# nested likely/unlikely calls
>>> +        if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>>> +            WARN("LIKELY_MISUSE",
>>
>> How do you think about to use the specification “(?:IS_ERR(?:_(?:OR_NULL|VALUE))?|WARN)”
>> in this regular expression?
…
>    IS_ERR
>    (?:_ <- Another atomic group just to show that '_' is a common prefix?

Yes. - I hope that this specification detail can help a bit.


>            Usually, Perl interpreter is very good at optimizing such things.

Would you like to help this software component by omitting a pair of
non-capturing parentheses at the beginning?

\b(?:un)?likely\s*


Regards,
Markus

Re: [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Denis Efremov]

On 31.08.2019 19:45, Markus Elfring wrote:
>>>> +# nested likely/unlikely calls
>>>> +        if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>>>> +            WARN("LIKELY_MISUSE",
>>>
>>> How do you think about to use the specification “(?:IS_ERR(?:_(?:OR_NULL|VALUE))?|WARN)”
>>> in this regular expression?
> …
>>    IS_ERR
>>    (?:_ <- Another atomic group just to show that '_' is a common prefix?
> 
> Yes. - I hope that this specification detail can help a bit.

I'm not sure that another pair of brackets for a single char worth it.

>>            Usually, Perl interpreter is very good at optimizing such things.

The interpreter optimizes it internally:
echo 'IS_ERR_OR_NULL' | perl -Mre=debug -ne '/IS_ERR(?:_OR_NULL|_VALUE)?/ && print'
Compiling REx "IS_ERR(?:_OR_NULL|_VALUE)?"
Final program:
   1: EXACT <IS_ERR> (4)
   4: CURLYX[0]{0,1} (16)
   6:   EXACT <_> (8)      <-- common prefix
   8:   TRIE-EXACT[OV] (15)
        <OR_NULL> 
        <VALUE>
...
> 
> Would you like to help this software component by omitting a pair of
> non-capturing parentheses at the beginning?
> 
> \b(?:un)?likely\s*

This pair of brackets is required to match "unlikely" and it's
optional in order to match "likely".

Regards,
Denis

Re: [PATCH v3 01/11] checkpatch: check for nested (un)?likely() calls

[Markus Elfring]

>>>>> +# nested likely/unlikely calls
>>>>> +        if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
>>>>> +            WARN("LIKELY_MISUSE",
…
>> \b(?:un)?likely\s*
>
> This pair of brackets is required to match "unlikely"
> and it's optional in order to match "likely".

I agree also to this view if you refer to the shortened regular expression here.
But I got an other development opinion for an extra pair of non-capturing parentheses
at the front (from the version which you suggested).

Regards,
Markus