Hi Geert-san,
> Sent: Thursday, October 01, 2015 4:22 PM
>
> If CONFIG_PREEMPT=y:
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000014
> pgd = c0003000
> [00000014] *pgd=80000040004003, *pmd=00000000
> Internal error: Oops: 206 [#1] PREEMPT SMP ARM
> Modules linked in:
> CPU: 0 PID: 17 Comm: kworker/0:1 Tainted: G W 4.3.0-rc3-koelsch-022
> 71-g705498fc5e6a5da8-dirty #1789
> Hardware name: Generic R8A7791 (Flattened Device Tree)
> Workqueue: pm pm_runtime_work
> task: ef578e40 ti: ef57a000 task.ti: ef57a000
> PC is at usb_dmac_chan_halt+0xc/0xc0
> LR is at usb_dmac_runtime_suspend+0x28/0x38
> pc : [<c023c880>] lr : [<c023c95c>] psr: 80000113
> sp : ef57bdf8 ip : 00000008 fp : 00000003
> r10: 00000008 r9 : c06ab928 r8 : ef49e810
> r7 : 00000000 r6 : 000000ac r5 : ef770010 r4 : 00000000
> r3 : 00000000 r2 : 8ffc2b84 r1 : 00000000 r0 : ef770010
> Flags: Nzcv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel
> Control: 30c5307d Table: 40003000 DAC: fffffffd
> Process kworker/0:1 (pid: 17, stack limit = 0xef57a210)
> Stack: (0xef57bdf8 to 0xef57c000)
>
> [...
>
> [<c023c880>] (usb_dmac_chan_halt) from [<c023c95c>] (usb_dmac_runtime_suspend+0x28/0x38)
> [<c023c95c>] (usb_dmac_runtime_suspend) from [<c027b25c>] (pm_genpd_runtime_suspend+0x74/0x23c)
>
> This happens because usb_dmac_probe() calls pm_runtime_put() before
> usb_dmac_chan_probe(), leading to the device being suspended before the
> DMA channels are initialized, causing a NULL pointer dereference.
>
> Move the call to pm_runtime_put() to the end of usb_dmac_probe() to fix
> this.
>
> Add a check to usb_dmac_runtime_suspend() to prevent the crash from
> happening in the error path.
>
> Reported-by: Sergei Shtylyov <sergei.shtylyov@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
I could not duplicate this issue completely on Lager.
Even if I enabled ealyprintk, I didn't see the panic log.
(Several kernel message appeared, and then the kernel hung.)
Anyway, I tested this patch that kernel could boot correctly even if CONFIG_PREEMPT=y.
So,
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
Best regards,
Yoshihiro Shimoda
> ---
> drivers/dma/sh/usb-dmac.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/sh/usb-dmac.c b/drivers/dma/sh/usb-dmac.c
> index ebd8a5f398b08ee2..f305738b5adf8cc9 100644
> --- a/drivers/dma/sh/usb-dmac.c
> +++ b/drivers/dma/sh/usb-dmac.c
> @@ -679,8 +679,11 @@ static int usb_dmac_runtime_suspend(struct device *dev)
> struct usb_dmac *dmac = dev_get_drvdata(dev);
> int i;
>
> - for (i = 0; i < dmac->n_channels; ++i)
> + for (i = 0; i < dmac->n_channels; ++i) {
> + if (!dmac->channels[i].iomem)
> + break;
> usb_dmac_chan_halt(&dmac->channels[i]);
> + }
>
> return 0;
> }
> @@ -803,7 +806,6 @@ static int usb_dmac_probe(struct platform_device *pdev)
> }
>
> ret = usb_dmac_init(dmac);
> - pm_runtime_put(&pdev->dev);
>
> if (ret) {
> dev_err(&pdev->dev, "failed to reset device\n");
> @@ -851,10 +853,12 @@ static int usb_dmac_probe(struct platform_device *pdev)
> if (ret < 0)
> goto error;
>
> + pm_runtime_put(&pdev->dev);
> return 0;
>
> error:
> of_dma_controller_free(pdev->dev.of_node);
> + pm_runtime_put(&pdev->dev);
> pm_runtime_disable(&pdev->dev);
> return ret;
> }
> --
> 1.9.1
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