Re: [PATCH] afs: use BIT_ULL for shifting to fix integer overflow

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To: Colin King <colin.king@xxxxxxxxxxxxx>
Subject: Re: [PATCH] afs: use BIT_ULL for shifting to fix integer overflow
From: David Howells <dhowells@xxxxxxxxxx>
Date: Fri, 30 Aug 2019 15:01:41 +0100
Cc: dhowells@xxxxxxxxxx, linux-afs@xxxxxxxxxxxxxxxxxxx, kernel-janitors@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20190830104912.1090-1-colin.king@canonical.com>
Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903
References: <20190830104912.1090-1-colin.king@canonical.com>

Colin King <colin.king@xxxxxxxxxxxxx> wrote:

> The expression 1 << nr_slots is evaluated with 32 bit integer arithmetic
> and can overflow before it is widened.

If it does, it's an error on the part of the caller.  See the banner comment:
1 <= nr_slots <= 9.

And, in any case, if nr_slots >= 64, using BIT_ULL wouldn't help...

David

Follow-Ups:
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  - From: Colin Ian King

References:
- [PATCH] afs: use BIT_ULL for shifting to fix integer overflow
  - From: Colin King

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