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

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Message-ID: <aRJASMinnNnUVc3Z@smile.fi.intel.com>
Date: Mon, 10 Nov 2025 21:43:04 +0200
From: "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: "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>,
	"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, Nov 10, 2025 at 07:37:13PM +0000, Viacheslav Dubeyko wrote:
> 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.

...

> > -	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?

Maybe. Or even maybe the U32_MAX is the way to go: Does anybody check those
corner cases? Are those never tested? Potential (security) bug?

...

Whatever you find, in case if it will be not the proposed solution as is,
consider these patches as Reported-by.

And thanks for the reviews!

-- 
With Best Regards,
Andy Shevchenko