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

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Message-ID: <c2805e34c4054bfa3308af0d18712e412f024ed6.camel@ibm.com>
Date: Mon, 10 Nov 2025 20:42:13 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>
CC: Xiubo Li <xiubli@...hat.com>,
        "justinstitt@...gle.com"
	<justinstitt@...gle.com>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        "ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nathan@...nel.org" <nathan@...nel.org>,
        "morbo@...gle.com"
	<morbo@...gle.com>,
        "idryomov@...il.com" <idryomov@...il.com>,
        "nick.desaulniers+lkml@...il.com" <nick.desaulniers+lkml@...il.com>
Subject: RE: [PATCH v1 1/1] ceph: Amend checking to fix `make W=1` build
 breakage

On Mon, 2025-11-10 at 21:43 +0200, andriy.shevchenko@...ux.intel.com wrote:
> 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!

I think we can take the patch as it. It looks good. Probably, it makes sense to
take a deeper look in the code on our side.

Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@....com>

Thanks,
Slava.