RE: [PATCH 1/2] soc: imx8: Fix potential kernel dump in error path

[Aisheng Dong]

> From: Anson.Huang@xxxxxxx [mailto:Anson.Huang@xxxxxxx]
> Sent: Wednesday, June 12, 2019 11:36 AM
> > 
> When SoC's revision value is 0, SoC driver will print out "unknown" in sysfs's
> revision node, this "unknown" is a static string which can NOT be freed, this
> will caused below kernel dump in later error path which calls kfree:
> 
> kernel BUG at mm/slub.c:3942!
> Internal error: Oops - BUG: 0 [#1] PREEMPT SMP Modules linked in:
> CPU: 2 PID: 1 Comm: swapper/0 Not tainted
> 5.2.0-rc4-next-20190611-00023-g705146c-dirty #2197 Hardware name: NXP
> i.MX8MQ EVK (DT)
> pstate: 60000005 (nZCv daif -PAN -UAO)
> pc : kfree+0x170/0x1b0
> lr : imx8_soc_init+0xc0/0xe4
> sp : ffff00001003bd10
> x29: ffff00001003bd10 x28: ffff00001121e0a0
> x27: ffff000011482000 x26: ffff00001117068c
> x25: ffff00001121e100 x24: ffff000011482000
> x23: ffff000010fe2b58 x22: ffff0000111b9ab0
> x21: ffff8000bd9dfba0 x20: ffff0000111b9b70
> x19: ffff7e000043f880 x18: 0000000000001000
> x17: ffff000010d05fa0 x16: ffff0000122e0000
> x15: 0140000000000000 x14: 0000000030360000
> x13: ffff8000b94b5bb0 x12: 0000000000000038
> x11: ffffffffffffffff x10: ffffffffffffffff
> x9 : 0000000000000003 x8 : ffff8000b9488147
> x7 : ffff00001003bc00 x6 : 0000000000000000
> x5 : 0000000000000003 x4 : 0000000000000003
> x3 : 0000000000000003 x2 : b8793acd604edf00
> x1 : ffff7e000043f880 x0 : ffff7e000043f888 Call trace:
>  kfree+0x170/0x1b0
>  imx8_soc_init+0xc0/0xe4
>  do_one_initcall+0x58/0x1b8
>  kernel_init_freeable+0x1cc/0x288
>  kernel_init+0x10/0x100
>  ret_from_fork+0x10/0x18
> 
> This patch fixes this potential kernel dump when a chip's revision is "unknown",
> it is done by always printing out the revision value.
> 
> Fixes: a7e26f356ca1 ("soc: imx: Add generic i.MX8 SoC driver")
> Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
> ---
>  drivers/soc/imx/soc-imx8.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/soc/imx/soc-imx8.c b/drivers/soc/imx/soc-imx8.c index
> 02309a2..86b925a 100644
> --- a/drivers/soc/imx/soc-imx8.c
> +++ b/drivers/soc/imx/soc-imx8.c
> @@ -96,11 +96,6 @@ static const struct of_device_id imx8_soc_match[] = {
>  	{ }
>  };
> 
> -#define imx8_revision(soc_rev) \
> -	soc_rev ? \
> -	kasprintf(GFP_KERNEL, "%d.%d", (soc_rev >> 4) & 0xf,  soc_rev & 0xf) : \
> -	"unknown"
> -
>  static int __init imx8_soc_init(void)
>  {
>  	struct soc_device_attribute *soc_dev_attr; @@ -135,7 +130,10 @@
> static int __init imx8_soc_init(void)
>  			soc_rev = data->soc_revision();
>  	}
> 
> -	soc_dev_attr->revision = imx8_revision(soc_rev);
> +	soc_dev_attr->revision = kasprintf(GFP_KERNEL,
> +					   "%d.%d",
> +					   (soc_rev >> 4) & 0xf,
> +					   soc_rev & 0xf);

The revision "0.0" is confusing.
I might prefer to check "unknown" before free.

Regards
Dong Aisheng

>  	if (!soc_dev_attr->revision) {
>  		ret = -ENOMEM;
>  		goto free_soc;
> --
> 2.7.4