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Date: Wed, 1 Apr 2026 07:32:18 -0700
From: "Darrick J. Wong" <djwong@kernel.org>
To: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Cc: Zorro Lang <zlang@redhat.com>, fstests@vger.kernel.org,
	Disha Goel <disgoel@linux.ibm.com>
Subject: Re: [PATCH 4/4] generic/775: Fix an infinite loop due to variable
 name clash
Message-ID: <20260401143218.GI6212@frogsfrogsfrogs>
References: <726e43008315a1bed018c1b43aae2458aebc03bc.1775039135.git.ojaswin@linux.ibm.com>
 <d1a7045002ded5d9e68347ff0fec41a86ff3877e.1775039135.git.ojaswin@linux.ibm.com>
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In-Reply-To: <d1a7045002ded5d9e68347ff0fec41a86ff3877e.1775039135.git.ojaswin@linux.ibm.com>

On Wed, Apr 01, 2026 at 04:10:50PM +0530, Ojaswin Mujoo wrote:
> We use i as the iteration variable in the main test loop as well as some
> internal loops. Due to this clash, $i variable of main test loops was
> getting modified by the following loop in prep_mixed_mapping().
> 
> 	for ((i=0; i<num_blocks; i++)); do
> 
> If num_blocks is less than 10 (example ext4 with blocksize 4k and
> cluster size 8k) i would always be set as 3 and the main loop would
> never exit. Take the simplest approach of just renaming the variable.
> 
> Reported-by: Disha Goel <disgoel@linux.ibm.com>
> Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> ---
>  tests/generic/775 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tests/generic/775 b/tests/generic/775
> index 2a4287bb..19ae95e2 100755
> --- a/tests/generic/775
> +++ b/tests/generic/775
> @@ -41,7 +41,7 @@ prep_mixed_mapping() {
>  
>  	local operations=("W" "H" "U")
>  	local num_blocks=$((awu_max / blksz))
> -	for ((i=0; i<num_blocks; i++)); do
> +	for ((j=0; j<num_blocks; j++)); do

You're right that the single-letter variables are a really bad idea in
languages like bash/python/etc where functions can see variables in
caller's scope if they're not explicitly marked local.

But a) why not use "local i" to prevent that; and (b) if you're going
to rename it, why not "blkno"?

--D

>  		local index=$((RANDOM % ${#operations[@]}))
>  		local map="${operations[$index]}"
>  		local mapping="${mapping}${map}"
> -- 
> 2.53.0
> 
>