linux-kernel - Re: [PATCH] lib/genaloc: Fix allocation of aligned buffer from non-aligned chunk

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Message-Id: <20181106141131.76e94f6b1ff2859d96792aca@linux-foundation.org>
Date:   Tue, 6 Nov 2018 14:11:31 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alexey Skidanov <alexey.skidanov@...el.com>
Cc:     sbates@...thlin.com, logang@...tatee.com, danielmentz@...gle.com,
        mathieu.desnoyers@...icios.com, linux-kernel@...r.kernel.org,
        labbott@...hat.com
Subject: Re: [PATCH] lib/genaloc: Fix allocation of aligned buffer from
 non-aligned chunk

On Tue,  6 Nov 2018 14:20:53 +0200 Alexey Skidanov <alexey.skidanov@...el.com> wrote:

> On success, gen_pool_first_fit_align() returns the bit number such that
> chunk_start_addr + (bit << order) is properly aligned. On failure,
> the bitmap size parameter is returned.
> 
> When the chunk_start_addr isn't aligned properly, the
> chunk_start_addr + (bit << order) isn't aligned too.
> 
> To fix this, gen_pool_first_fit_align() takes into account
> the chunk_start_addr alignment and returns the bit value such that
> chunk_start_addr + (bit << order) is properly aligned
> (exactly as it done in CMA).

Why does this need "fixing"?  Are there current callers which can
misalign chunk_start_addr?  Or is there a requirement that future
callers can misalign chunk_start_addr?