linux-kernel - Re: [PATCH] locking/lock_events: no need to check return value of debugfs

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Message-ID: <20201109083251.GA2594@hirez.programming.kicks-ass.net>
Date:   Mon, 9 Nov 2020 09:32:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        linux-kernel@...r.kernel.org, Xuefeng Li <lixuefeng@...ngson.cn>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] locking/lock_events: no need to check return value of
 debugfs_create functions

On Sat, Nov 07, 2020 at 05:19:13PM +0800, Tiezhu Yang wrote:
> When calling debugfs functions, there is no need to ever check the
> return value.  The function can work or not, but the code logic should
> never do something different based on this.

I strongly disagree and have told this to Greg before. Having half a
debug interface is weird at best, so upon failure we remove the whole
thing, which is consistent.

> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>  kernel/locking/lock_events.c | 19 ++++---------------
>  1 file changed, 4 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/locking/lock_events.c b/kernel/locking/lock_events.c
> index fa2c2f9..bac77a1 100644
> --- a/kernel/locking/lock_events.c
> +++ b/kernel/locking/lock_events.c
> @@ -146,9 +146,6 @@ static int __init init_lockevent_counts(void)
>  	struct dentry *d_counts = debugfs_create_dir(LOCK_EVENTS_DIR, NULL);
>  	int i;
>  
> -	if (!d_counts)
> -		goto out;
> -
>  	/*
>  	 * Create the debugfs files
>  	 *
> @@ -159,21 +156,13 @@ static int __init init_lockevent_counts(void)
>  	for (i = 0; i < lockevent_num; i++) {
>  		if (skip_lockevent(lockevent_names[i]))
>  			continue;
> -		if (!debugfs_create_file(lockevent_names[i], 0400, d_counts,
> -					 (void *)(long)i, &fops_lockevent))
> -			goto fail_undo;
> +		debugfs_create_file(lockevent_names[i], 0400, d_counts,
> +				    (void *)(long)i, &fops_lockevent);
>  	}
>  
> -	if (!debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200,
> -				 d_counts, (void *)(long)LOCKEVENT_reset_cnts,
> -				 &fops_lockevent))
> -		goto fail_undo;
> +	debugfs_create_file(lockevent_names[LOCKEVENT_reset_cnts], 0200, d_counts,
> +			    (void *)(long)LOCKEVENT_reset_cnts, &fops_lockevent);
>  
>  	return 0;
> -fail_undo:
> -	debugfs_remove_recursive(d_counts);
> -out:
> -	pr_warn("Could not create '%s' debugfs entries\n", LOCK_EVENTS_DIR);
> -	return -ENOMEM;
>  }
>  fs_initcall(init_lockevent_counts);
> -- 
> 2.1.0
>