Re: [PATCH] ext4: Remove unreachable code

From: Andreas Dilger <adilger@dilger.ca>
To: Vinicius Tinti <viniciustinti@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com
Subject: Re: [PATCH] ext4: Remove unreachable code
Date: Fri, 29 Jan 2021 23:42:20 -0700	[thread overview]
Message-ID: <AAB32610-D238-4137-96DE-33655AAAB545@dilger.ca> (raw)
In-Reply-To: <20210129185856.158310-1-viniciustinti@gmail.com>

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On Jan 29, 2021, at 11:58 AM, Vinicius Tinti <viniciustinti@gmail.com> wrote:
> 
> By enabling -Wunreachable-code-aggressive on Clang the following code
> paths are unreachable.
> 
> Commit dd73b5d5cb67 ("ext4: convert dx_probe() to use the ERR_PTR
> convention")
> Commit ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3")
> 
> Clang warns:
> 
> fs/ext4/namei.c:831:17: warning: code will never be executed
> [-Wunreachable-code]
>                        unsigned n = count - 1;
>                                     ^~~~~
> fs/ext4/namei.c:830:7: note: silence by adding parentheses to mark code as
> explicitly dead
>                if (0) { // linear search cross check
>                    ^
>                    /* DISABLES CODE */ ( )
> 
> Signed-off-by: Vinicius Tinti <viniciustinti@gmail.com>
> ---
> fs/ext4/namei.c | 15 ---------------
> 1 file changed, 15 deletions(-)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index cf652ba3e74d..1f64dbd7237b 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -827,21 +827,6 @@ dx_probe(struct ext4_filename *fname, struct inode *dir,
> 				p = m + 1;
> 		}
> 
> -		if (0) { // linear search cross check

I would rather put this block under "#ifdef DX_DEBUG" so that it is available
in the future for debugging problems with hashed directories.

> -			unsigned n = count - 1;
> -			at = entries;
> -			while (n--)
> -			{
> -				dxtrace(printk(KERN_CONT ","));
> -				if (dx_get_hash(++at) > hash)
> -				{
> -					at--;
> -					break;
> -				}
> -			}
> -			ASSERT(at == p - 1);
> -		}
> -
> 		at = p - 1;
> 		dxtrace(printk(KERN_CONT " %x->%u\n",
> 			       at == entries ? 0 : dx_get_hash(at),
> --
> 2.25.1
> 

Cheers, Andreas

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