linux-kernel - Re: [PATCH] rapidio: use a reference count for struct mport_dma

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Date:   Mon, 9 Apr 2018 15:39:36 -0400
From:   Alex Bounine <alex.bou9@...il.com>
To:     Ioan Nicu <ioan.nicu.ext@...ia.com>,
        Andrew Morton <akpm@...uxfoundation.org>,
        Barry Wood <barry.wood@....com>,
        Matt Porter <mporter@...nel.crashing.org>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Al Viro <viro@...iv.linux.org.uk>,
        Logan Gunthorpe <logang@...tatee.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>,
        Frank Kunz <frank.kunz@...ia.com>,
        Alexander Sverdlin <alexander.sverdlin@...ia.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rapidio: use a reference count for struct mport_dma_req


On 2018-04-05 04:33 PM, Ioan Nicu wrote:
> Once the dma request is passed to the DMA engine, the DMA
> subsystem would hold a pointer to this structure and could
> call the completion callback after do_dma_request() has
> timed out.
> 
> The current code deals with this by putting timed out SYNC
> requests to a pending list and freeing them later, when the
> mport cdev device is released. But this still does not
> guarantee that the DMA subsystem is really done with those
> transfers, so in theory dma_xfer_callback/dma_req_free
> could be called after mport_cdev_release_dma and could
> potentially access already freed memory.
> 
> This patch simplifies the current handling by using a kref
> in the mport dma request structure, so that it gets freed
> only when nobody uses it anymore.
> 
> This also simplifies the code a bit, as FAF transfers are
> now handled in the same way as SYNC and ASYNC transfers.
> There is no need anymore for the pending list and for the
> dma workqueue which was used in case of FAF transfers, so
> we remove them both.
> 
> Signed-off-by: Ioan Nicu <ioan.nicu.ext@...ia.com>
> ---
>   drivers/rapidio/devices/rio_mport_cdev.c | 122 +++++--------------------------
>   1 file changed, 18 insertions(+), 104 deletions(-)

Acked-by: Alexandre Bounine <alex.bou9@...il.com>