linux-kernel - Re: [PATCH 03/18] fs_context: fix detecting full log buffer

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Message-ID: <10922.1531128946@warthog.procyon.org.uk>
Date:   Mon, 09 Jul 2018 10:35:46 +0100
From:   David Howells <dhowells@...hat.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     dhowells@...hat.com, Eric Biggers <ebiggers3@...il.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH 03/18] fs_context: fix detecting full log buffer

David Howells <dhowells@...hat.com> wrote:

> > When 'head' and 'tail' wrap around, 'log->head - log->tail' will be
> > something like '4 - 252 = -248', and comparing that directly to the
> > array size is wrong.  Fix by casting to 'u8'.
> 
> I think a better fix is to use CIRC_CNT() or CIRC_SPACE().

Or it would be - if CIRC_CNT() and CIRC_SPACE() didn't leave a hole in the
buffer - but that's unnecessary if the head and tail counters can hold 2x the
ring size or more.

David