linux-kernel - Re: [PATCH v1 1/1] ceph: Amend checking to fix `make W=1` build breakage

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Message-ID: <9f7339a71c281e9f9e5b1ff34f7c277f62c89a69.camel@ibm.com>
Date: Mon, 10 Nov 2025 19:37:13 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "nathan@...nel.org" <nathan@...nel.org>,
        "justinstitt@...gle.com"
	<justinstitt@...gle.com>,
        Xiubo Li <xiubli@...hat.com>,
        "idryomov@...il.com"
	<idryomov@...il.com>,
        "nick.desaulniers+lkml@...il.com"
	<nick.desaulniers+lkml@...il.com>,
        "morbo@...gle.com" <morbo@...gle.com>
Subject: Re:  [PATCH v1 1/1] ceph: Amend checking to fix `make W=1` build
 breakage

On Mon, 2025-11-10 at 15:44 +0100, Andy Shevchenko wrote:
> In a few cases the code compares 32-bit value to a SIZE_MAX derived
> constant which is much higher than that value on 64-bit platforms,
> Clang, in particular, is not happy about this
> 
> fs/ceph/snap.c:377:10: error: result of comparison of constant 2305843009213693948 with expression of type 'u32' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>   377 |         if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
>       |             ~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Fix this by casting to size_t. Note, that possible replacement of SIZE_MAX
> by U32_MAX may lead to the behaviour changes on the corner cases.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  fs/ceph/snap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index c65f2b202b2b..521507ea8260 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -374,7 +374,7 @@ static int build_snap_context(struct ceph_mds_client *mdsc,
>  
>  	/* alloc new snap context */
>  	err = -ENOMEM;
> -	if (num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))
> +	if ((size_t)num > (SIZE_MAX - sizeof(*snapc)) / sizeof(u64))

The same question is here. Does it makes sense to declare num as size_t? Could
it be more clean solution? Or could it introduce another warnings/errors?

Thanks,
Slava.

>  		goto fail;
>  	snapc = ceph_create_snap_context(num, GFP_NOFS);
>  	if (!snapc)