linux-kernel - Re: [qemu] boot failed: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

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Date:   Mon, 6 Jul 2020 20:40:41 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        linux-serial@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>, jirislaby@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        ldewangan@...dia.com, Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>, Qian Cai <cai@....pw>,
        lkft-triage@...ts.linaro.org
Subject: Re: [qemu] boot failed: Unable to handle kernel NULL pointer
 dereference at virtual address 0000000000000000

On 06-07-20, 07:33, Dave Jiang wrote:

> > I don't see anything suspicious in dmaengine drivers, but there is a
> > recent series
> > from Dave Jiang that might explain it. Could you try reverting  commit
> > deb9541f5052 ("dmaengine: check device and channel list for empty")?
> > 
> > I think the broken change is this one:
> > 
> > @@ -819,6 +850,11 @@ struct dma_chan *dma_request_chan(struct device
> > *dev, const char *name)
> > 
> >          /* Try to find the channel via the DMA filter map(s) */
> >          mutex_lock(&dma_list_mutex);
> > +       if (list_empty(&dma_device_list)) {
> > +               mutex_unlock(&dma_list_mutex);
> > +               return NULL;
> > +       }
> > +
> >          list_for_each_entry_safe(d, _d, &dma_device_list, global_node) {
> >                  dma_cap_mask_t mask;
> >                  const struct dma_slave_map *map = dma_filter_match(d,
> > name, dev);
> > 
> > which needs to return an error code like -ENODEV instead of NULL. There
> > may be other changes in the same patch that introduce the same bug
> > elsewhere.
> > 
> >       Arnd
> > 
> 
> Vinod,
> Do you want a diff fix or a revision of the patch for the fix?

Diff fix please

-- 
~Vinod