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References: <20220830093439.951960-1-koba.ko@canonical.com> <c3ea3992-df42-3a26-6d30-834368faf91c@amd.com>
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From:   Koba Ko <koba.ko@canonical.com>
Date:   Wed, 31 Aug 2022 13:39:00 +0800
Message-ID: <CAJB-X+XMHYyQJLLuC24rAvQwNOOZUdMBhh12RC9UTOSCrCa=HA@mail.gmail.com>
Subject: Re: crypto: ccp - Release dma channels before dmaengine unrgister
To:     Tom Lendacky <thomas.lendacky@amd.com>
Cc:     John Allen <john.allen@amd.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
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Precedence: bulk

On Tue, Aug 30, 2022 at 11:32 PM Tom Lendacky <thomas.lendacky@amd.com> wrote:
>
> On 8/30/22 04:34, Koba Ko wrote:
> > A warning is shown during shutdown,
> >
> > __dma_async_device_channel_unregister called while 2 clients hold a reference
> > WARNING: CPU: 15 PID: 1 at drivers/dma/dmaengine.c:1110
> > __dma_async_device_channel_unregister
> >
> > Call dma_release_channel for occupied channles
> > before dma_async_device_unregister.
> >
> > Fixes: 4cbe9bc34ed0 ("crypto: ccp - ccp_dmaengine_unregister release dma channels")
> > Signed-off-by: Koba Ko <koba.ko@canonical.com>
> > ---
> >   drivers/crypto/ccp/ccp-dmaengine.c | 8 +++++++-
> >   1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/crypto/ccp/ccp-dmaengine.c b/drivers/crypto/ccp/ccp-dmaengine.c
> > index 7d4b4ad1db1f3..ba3eb1ac3b55d 100644
> > --- a/drivers/crypto/ccp/ccp-dmaengine.c
> > +++ b/drivers/crypto/ccp/ccp-dmaengine.c
> > @@ -641,6 +641,10 @@ static void ccp_dma_release(struct ccp_device *ccp)
> >       for (i = 0; i < ccp->cmd_q_count; i++) {
> >               chan = ccp->ccp_dma_chan + i;
> >               dma_chan = &chan->dma_chan;
> > +
> > +             if (dma_chan->client_count)
> > +                     dma_release_channel(dma_chan);
> > +
> >               tasklet_kill(&chan->cleanup_tasklet);
> >               list_del_rcu(&dma_chan->device_node);
> >       }
> > @@ -762,12 +766,14 @@ int ccp_dmaengine_register(struct ccp_device *ccp)
> >   void ccp_dmaengine_unregister(struct ccp_device *ccp)
> >   {
> >       struct dma_device *dma_dev = &ccp->dma_dev;
> > +     struct dma_chan *dma_chan;
> > +     unsigned int i;
> >
> >       if (!dmaengine)
> >               return;
> >
> > -     dma_async_device_unregister(dma_dev);
> >       ccp_dma_release(ccp);
> > +     dma_async_device_unregister(dma_dev);
>
> Seems the right way to get rid of the warn, but can there still be a race
> where the channel is grabbed again after ccp_dma_release() and before
> dma_async_device_unregister() is called?

After tracing the ccp driver,
dma_device is held by the ccp device.
the only function called ccp_dmaengine_register is ccp5_init/ccp_init,
ccp_dma_release is called in ccp_dmaengine_unregister/ccp_dmaengine_register,
so there's no race condition in current codes.


>
> Thanks,
> Tom
>
> >
> >       kmem_cache_destroy(ccp->dma_desc_cache);
> >       kmem_cache_destroy(ccp->dma_cmd_cache);