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

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Message-ID: <20210119180327.GX4605@ziepe.ca>
Date:   Tue, 19 Jan 2021 14:03:27 -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 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

It looks like it would not be so bad to implement some
check_round_up_overflow() if people prefer

Jason