linux-kernel - Re: [PATCH] [v2] jfs: avoid -Wtautological-constant-out-of-range-compare warning

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Message-ID: <fb9e19bd-2543-4b83-9ec4-f595afd358c8@oracle.com>
Date: Mon, 2 Feb 2026 15:40:44 -0600
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Arnd Bergmann <arnd@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
        Zheng Yu <zheng.yu@...thwestern.edu>
Cc: Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
        Bill Wendling <morbo@...gle.com>,
        Justin Stitt <justinstitt@...gle.com>,
        Roman Smirnov <r.smirnov@....ru>, Aditya Dutt <duttaditya18@...il.com>,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] [v2] jfs: avoid
 -Wtautological-constant-out-of-range-compare warning

On 2/2/26 2:43PM, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> A recent change for the range check started triggering a clang warning:
> 
> fs/jfs/jfs_dtree.c:2906:31: error: result of comparison of constant 128 with expression of type 's8' (aka 'signed char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>   2906 |                         if (stbl[i] < 0 || stbl[i] >= DTPAGEMAXSLOT) {
>        |                                            ~~~~~~~ ^  ~~~~~~~~~~~~~
> fs/jfs/jfs_dtree.c:3111:30: error: result of comparison of constant 128 with expression of type 's8' (aka 'signed char') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>   3111 |                 if (stbl[0] < 0 || stbl[0] >= DTPAGEMAXSLOT) {
>        |                                    ~~~~~~~ ^  ~~~~~~~~~~~~~
> 
> Both the old and the new check were useless, but the previous version
> apparently did not lead to the warning.
> 
> Remove the extraneous range check for simplicity.
> 
> Fixes: cafc6679824a ("jfs: replace hardcoded magic number with DTPAGEMAXSLOT constant")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: drop the check instead of shutting up the warning

Looks good. I'll put this into jfs-next.

> ---
>   fs/jfs/jfs_dtree.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jfs/jfs_dtree.c b/fs/jfs/jfs_dtree.c
> index 0ab83bb7bbdf..9ab3f2fc61d1 100644
> --- a/fs/jfs/jfs_dtree.c
> +++ b/fs/jfs/jfs_dtree.c
> @@ -2903,7 +2903,7 @@ int jfs_readdir(struct file *file, struct dir_context *ctx)
>   		stbl = DT_GETSTBL(p);
>   
>   		for (i = index; i < p->header.nextindex; i++) {
> -			if (stbl[i] < 0 || stbl[i] >= DTPAGEMAXSLOT) {
> +			if (stbl[i] < 0) {
>   				jfs_err("JFS: Invalid stbl[%d] = %d for inode %ld, block = %lld",
>   					i, stbl[i], (long)ip->i_ino, (long long)bn);
>   				free_page(dirent_buf);
> @@ -3108,7 +3108,7 @@ static int dtReadFirst(struct inode *ip, struct btstack * btstack)
>   		/* get the leftmost entry */
>   		stbl = DT_GETSTBL(p);
>   
> -		if (stbl[0] < 0 || stbl[0] >= DTPAGEMAXSLOT) {
> +		if (stbl[0] < 0) {
>   			DT_PUTPAGE(mp);
>   			jfs_error(ip->i_sb, "stbl[0] out of bound\n");
>   			return -EIO;