linux-kernel - Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places

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Message-ID: <23535.1523453966@warthog.procyon.org.uk>
Date:   Wed, 11 Apr 2018 14:39:26 +0100
From:   David Howells <dhowells@...hat.com>
To:     Colin King <colin.king@...onical.com>
Cc:     dhowells@...hat.com, linux-afs@...ts.infradead.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] afs: fix integer overflow when shifting 1 more than 32 places

Colin King <colin.king@...onical.com> wrote:

> Shifting 1 (a 32 bit signed int) more than 32 places will overflow
> the int, so explicitly use 1ULL to avoid this overflow.
> ...
> -	mask = (1 << nr_slots) - 1;
> +	mask = (1ULL << nr_slots) - 1;

nr_slots cannot be larger than 9, so what I wrote is actually fine and is more
efficient on a 32-bit machine.

David