linux-kernel - Re: [PATCH v6 1/4] sgl_alloc_order: remove 4 GiB limit, sgl

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Message-ID: <20210119181714.GA909645@ziepe.ca>
Date:   Tue, 19 Jan 2021 14:17:14 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Bodo Stroesser <bostroesser@...il.com>
Cc:     Douglas Gilbert <dgilbert@...erlog.com>,
        linux-scsi@...r.kernel.org, linux-block@...r.kernel.org,
        target-devel@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, martin.petersen@...cle.com,
        jejb@...ux.vnet.ibm.com, ddiss@...e.de, bvanassche@....org
Subject: Re: [PATCH v6 1/4] sgl_alloc_order: remove 4 GiB limit, sgl_free()
 warning

On Tue, Jan 19, 2021 at 07:08:32PM +0100, Bodo Stroesser wrote:
> On 19.01.21 19:03, Jason Gunthorpe wrote:
> > On Tue, Jan 19, 2021 at 06:24:49PM +0100, Bodo Stroesser wrote:
> > > 
> > > I had a second look into math.h, but I don't find any reason why round_up
> > > could overflow. Can you give a hint please?
> > 
> > #define round_up(x, y) ((((x)-1) | __round_mask(x, y))+1)
> >                                                      ^^^^^
> > 
> > That +1 can overflow
> 
> But that would be a unsigned long long overflow. I considered this to
> not be relevant.

Why not? It still makes nents 0 and still causes a bad bug

Jason