Re: [PATCH v2 2/3] spi: Use bus_type functions for probe, remove and shutdown

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

Hi Uwe,

On 19.11.2020 17:16, Uwe Kleine-König wrote:
> The eventual goal is to get rid of the callbacks in struct
> device_driver. Other than not using driver callbacks there should be no
> side effect of this patch.
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>

This patch landed recently in linux-next as commit 9db34ee64ce4 ("spi: 
Use bus_type functions for probe, remove and shutdown").

It causes a regression on some of my test boards:

Unable to handle kernel NULL pointer dereference at virtual address 
0000000000000018
Mem abort info:
   ESR = 0x96000004
   EC = 0x25: DABT (current EL), IL = 32 bits
   SET = 0, FnV = 0
   EA = 0, S1PTW = 0
Data abort info:
   ISV = 0, ISS = 0x00000004
   CM = 0, WnR = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=00000000318ed000
[0000000000000018] pgd=0000000000000000, p4d=0000000000000000
Internal error: Oops: 96000004 [#1] PREEMPT SMP
Modules linked in: cpufreq_powersave cpufreq_conservative brcmfmac 
brcmutil cfg80211 crct10dif_ce s3fwrn5_i2c s3fwrn5 nci nfc s5p_mfc 
s5p_jpeg hci_uart btqca btbc
buf2_dma_contig videobuf2_memops videobuf2_v4l2 bluetooth 
videobuf2_common videodev panfrost gpu_sched ecdh_generic mc ecc rfkill 
ip_tables x_tables ipv6
CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 
5.10.0-rc5-next-20201124+ #9771
Hardware name: Samsung TM2E board (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--)
pc : spi_shutdown+0x10/0x38
lr : device_shutdown+0x10c/0x350
sp : ffff80001311bc70
...
Call trace:
  spi_shutdown+0x10/0x38
  kernel_restart_prepare+0x34/0x40
  kernel_restart+0x14/0x88
  __do_sys_reboot+0x148/0x248
  __arm64_sys_reboot+0x1c/0x28
  el0_svc_common.constprop.3+0x74/0x198
  do_el0_svc+0x20/0x98
  el0_sync_handler+0x140/0x1a8
  el0_sync+0x140/0x180
Code: f9403402 d1008041 f100005f 9a9f1021 (f9400c21)
---[ end trace 266c07205a2d632e ]---
Kernel panic - not syncing: Oops: Fatal exception
Kernel Offset: disabled
CPU features: 0x0240022,65006087
Memory Limit: none
---[ end Kernel panic - not syncing: Oops: Fatal exception ]---

> ---
>   drivers/spi/spi.c | 33 ++++++++++++++++-----------------
>   1 file changed, 16 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index 5becf6c2c409..e8c0a000ee19 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -374,16 +374,7 @@ static int spi_uevent(struct device *dev, struct kobj_uevent_env *env)
>   	return add_uevent_var(env, "MODALIAS=%s%s", SPI_MODULE_PREFIX, spi->modalias);
>   }
>   
> -struct bus_type spi_bus_type = {
> -	.name		= "spi",
> -	.dev_groups	= spi_dev_groups,
> -	.match		= spi_match_device,
> -	.uevent		= spi_uevent,
> -};
> -EXPORT_SYMBOL_GPL(spi_bus_type);
> -
> -
> -static int spi_drv_probe(struct device *dev)
> +static int spi_probe(struct device *dev)
>   {
>   	const struct spi_driver		*sdrv = to_spi_driver(dev->driver);
>   	struct spi_device		*spi = to_spi_device(dev);
> @@ -414,7 +405,7 @@ static int spi_drv_probe(struct device *dev)
>   	return ret;
>   }
>   
> -static int spi_drv_remove(struct device *dev)
> +static int spi_remove(struct device *dev)
>   {
>   	const struct spi_driver		*sdrv = to_spi_driver(dev->driver);
>   	int ret = 0;
> @@ -426,13 +417,25 @@ static int spi_drv_remove(struct device *dev)
>   	return ret;
>   }
>   
> -static void spi_drv_shutdown(struct device *dev)
> +static void spi_shutdown(struct device *dev)
>   {
>   	const struct spi_driver		*sdrv = to_spi_driver(dev->driver);
>   
> -	sdrv->shutdown(to_spi_device(dev));
> +	if (sdrv->shutdown)
> +		sdrv->shutdown(to_spi_device(dev));
>   }

In the above function dev->driver might be NULL, so its use in 
to_spi_driver() and sdrv->shutdown leads to NULL pointer dereference. I 
didn't check the details, but a simple check for NULL dev->driver and 
return is enough to fix this issue. I can send such fix if you want.

> +struct bus_type spi_bus_type = {
> +	.name		= "spi",
> +	.dev_groups	= spi_dev_groups,
> +	.match		= spi_match_device,
> +	.uevent		= spi_uevent,
> +	.probe		= spi_probe,
> +	.remove		= spi_remove,
> +	.shutdown	= spi_shutdown,
> +};
> +EXPORT_SYMBOL_GPL(spi_bus_type);
> +
>   /**
>    * __spi_register_driver - register a SPI driver
>    * @owner: owner module of the driver to register
> @@ -445,10 +448,6 @@ int __spi_register_driver(struct module *owner, struct spi_driver *sdrv)
>   {
>   	sdrv->driver.owner = owner;
>   	sdrv->driver.bus = &spi_bus_type;
> -	sdrv->driver.probe = spi_drv_probe;
> -	sdrv->driver.remove = spi_drv_remove;
> -	if (sdrv->shutdown)
> -		sdrv->driver.shutdown = spi_drv_shutdown;
>   	return driver_register(&sdrv->driver);
>   }
>   EXPORT_SYMBOL_GPL(__spi_register_driver);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland