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

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Message-ID: <24493.1523455816@warthog.procyon.org.uk>
Date:   Wed, 11 Apr 2018 15:10:16 +0100
From:   David Howells <dhowells@...hat.com>
To:     Colin Ian 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 Ian King <colin.king@...onical.com> wrote:

> >> -	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.
> 
> ok, sorry about the noise.

It would be possible to cast the value to u64 before assigning it, I suppose.
Would that help?  E.g.:

	mask = (u64)((1 << nr_slots) - 1);

It looks a bit odd, though, since the cast is made implicitly anyway.

David