linux-kernel - Re: dma_zalloc_coherent broken with 57bf5a8963f80fb3828c46c3e3a5b2dd790e09a7

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Message-ID: <20180327143341.GA4968@lst.de>
Date:   Tue, 27 Mar 2018 16:33:41 +0200
From:   Christoph Hellwig <hch@....de>
To:     Sebastian Ott <sebott@...ux.vnet.ibm.com>
Cc:     Christoph Hellwig <hch@....de>,
        Jesper Nilsson <jesper.nilsson@...s.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-kernel@...r.kernel.org
Subject: Re: dma_zalloc_coherent broken with
        57bf5a8963f80fb3828c46c3e3a5b2dd790e09a7

On Tue, Mar 27, 2018 at 10:12:54AM +0200, Sebastian Ott wrote:
> Hi,
> 
> commit 57bf5a8963f80fb3828c46c3e3a5b2dd790e09a7 broke usage of dma
> allocations specifying __GFP_ZERO by silently removing that flag.
> 
> Why should "the memory returned [] always be zeroed."?

Because that is what the current implementations do - we always zero
the memory returned from dma_map_ops.alloc().