Re: [PATCH] media: videobuf2: fix kernel panic due to missing assign NULL to alloc_ctx

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Albert,

On Friday 08 June 2012 19:55:11 Albert Wang wrote:
>   In function vb2_dma_contig_cleanup_ctx(), we only kfree the alloc_ctx
>   If we didn't assign NULL to this point after kfree it,
>   we may encounter the following kernel panic:
> 
>  kernel BUG at kernel/cred.c:98!
>  Unable to handle kernel NULL pointer dereference at virtual address
> 00000000 pgd = c0004000
>  [00000000] *pgd=00000000
>  Internal error: Oops: 817 [#1] PREEMPT SMP
>  Modules linked in: runcase_sysfs galcore mv_wtm_drv mv_wtm_prim
>  CPU: 0    Not tainted  (3.0.8+ #213)
>  PC is at __bug+0x18/0x24
>  LR is at __bug+0x14/0x24
>  pc : [<c0054670>]    lr : [<c005466c>]    psr: 60000113
>  sp : c0681ec0  ip : f683e000  fp : 00000000
>  r10: e8ab4b58  r9 : 00000fff  r8 : 00000002
>  r7 : e8665698  r6 : c10079ec  r5 : e8b13d80  r4 : e8b13d98
>  r3 : 00000000  r2 : c0681eb4  r1 : c05c9ccc  r0 : 00000035
>  Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
>  Control: 10c53c7d  Table: 29c3406a  DAC: 00000015
> 
>   the root cause is we may encounter some i2c or HW issue with sensor
>   which result in driver exit with exception during soc_camera_set_fmt()
>   from soc_camera_open():
> 
> 	ret = soc_camera_set_fmt(icd, &f);
> 	if (ret < 0)
> 		goto esfmt;
> 
>   it will call ici->ops->remove() in following code:
> 
>   esfmt:
> 	pm_runtime_disable(&icd->vdev->dev);
>   eresume:
> 	ici->ops->remove(icd);
> 
>   ici->ops->remove() will call vb2_dma_contig_cleanup_ctx() for cleanup
>   but we didn't do ici->ops->init_videobuf2() yet at that time
>   it will result in kfree a non-NULL point twice

I'm not sure to follow you. How is init_videobuf2() related ? The context is 
allocated once only at probe time from what I can see. Your problem is more 
likely caused by a double call to vb2_dma_contig_cleanup_ctx(), which looks 
like a driver bug to me, not a videobuf2 bug.

> Change-Id: I1c66dd08438ae90abe555c52edcdbca0d39d829d
> Signed-off-by: Albert Wang <twang13@marvell.com>
> ---
>  drivers/media/video/videobuf2-dma-contig.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/media/video/videobuf2-dma-contig.c
> b/drivers/media/video/videobuf2-dma-contig.c index 4b71326..9881171 100755
> --- a/drivers/media/video/videobuf2-dma-contig.c
> +++ b/drivers/media/video/videobuf2-dma-contig.c
> @@ -178,6 +178,7 @@ EXPORT_SYMBOL_GPL(vb2_dma_contig_init_ctx);
>  void vb2_dma_contig_cleanup_ctx(void *alloc_ctx)
>  {
>  	kfree(alloc_ctx);
> +	alloc_ctx = NULL;
>  }
>  EXPORT_SYMBOL_GPL(vb2_dma_contig_cleanup_ctx);

-- 
Regards,

Laurent Pinchart