linux-kernel - Re: checkpatch.pl: WARNING: else is not generally useful after a break or return

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Date:   Fri, 17 Apr 2020 12:56:03 -0700
From:   Joe Perches <joe@...ches.com>
To:     Luben Tuikov <luben.tuikov@....com>,
        Andy Whitcroft <apw@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: checkpatch.pl: WARNING: else is not generally useful after a
 break or return

On Fri, 2020-04-17 at 15:20 -0400, Luben Tuikov wrote:
> Hi,
> 
> I'm getting what seems to be a false positive in this case:
> 
> :32: WARNING: else is not generally useful after a break or return
> #32: FILE: drivers/gpu/drm/amd/amdgpu/amdgpu_job.c:55:
> +		return 0;
> +	} else {
> 
> for the following code, at the bottom of a function:
> 
> 	if (amdgpu_device_should_recover_gpu(ring->adev)) {
> 		amdgpu_device_gpu_recover(ring->adev, job);
> 		return 0;
> 	} else {
> 		drm_sched_suspend_timeout(&ring->sched);
> 		return 1;
> 	}
> }
> 
> Which seems to be coming from commit:
> 
> commit 032a4c0f9a77ce565355c6e191553e853ba66f09
> Author: Joe Perches <joe@...ches.com>
> Date:   Wed Aug 6 16:10:29 2014 -0700
> 
>     checkpatch: warn on unnecessary else after return or break
>     
>     Using an else following a break or return can unnecessarily indent code
>     blocks.
>     
>     ie:
>             for (i = 0; i < 100; i++) {
>                     int foo = bar();
>                     if (foo < 1)
>                             break;
>                     else
>                             usleep(1);
>             }
>     
>     is generally better written as:
>     
>             for (i = 0; i < 100; i++) {
>                     int foo = bar();
>                     if (foo < 1)
>                             break;
>                     usleep(1);
>             }
>     
>     Warn when a bare else statement is preceded by a break or return
>     indented 1 tab more than the else.
>     
>     Signed-off-by: Joe Perches <joe@...ches.com>
>     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>     Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> 
> While I agree with what the commit is trying to do,
> it doesn't seem to apply to the if-else statement which I quoted
> above. That is, the "else" is not "bare"--to use the lingo of
> the commit.
> 
> I suggest that no warning is issued when the "else" is a compound
> statement, as shown in my example at the top of this email.
> 
> It is only natural to write:
> 
> 	if (amdgpu_device_should_recover_gpu(ring->adev)) {
> 		amdgpu_device_gpu_recover(ring->adev, job);
> 		return 0;
> 	} else {
> 		drm_sched_suspend_timeout(&ring->sched);
> 		return 1;
> 	}
> }
> 
> instead of,
> 
> 	if (amdgpu_device_should_recover_gpu(ring->adev)) {
> 		amdgpu_device_gpu_recover(ring->adev, job);
> 		return 0;
> 	}
> 	drm_sched_suspend_timeout(&ring->sched);
> 	return 1;
> }

This is continuing an email thread sent privately to Andy and me.

I disagree and do not believe this should be implemented in
checkpatch as an accepted typical coding style.

btw:

Even in your example, amdgpu_device_gpu_recover has a return
value, can fail, and likely should not just return 0.