[PATCH] ath6kl: sdio: fix system panic when doing wifi stress test

[Hui Liu]

> -----Original Message-----
> From: Kalle Valo [mailto:kvalo at qca.qualcomm.com]
> Sent: Tuesday, November 26, 2013 6:40 PM
> To: Liu Hui-R64343
> Cc: linux-arm-kernel at lists.infradead.org; linville at tuxdriver.com; linux-
> wireless at vger.kernel.org; netdev at vger.kernel.org; linux-
> kernel at vger.kernel.org; ath6kl-devel at qca.qualcomm.com
> Subject: Re: [PATCH] ath6kl: sdio: fix system panic when doing wifi
> stress test
> 
> Hi Jason,
> 
> Jason Liu <r64343 at freescale.com> writes:
> 
> > When did the wifi iperf test, meet one following kernel panic:
> > command: iperf -c $TARGET_IP -i 5 -t 50 -w 1M
> >
> > Unable to handle kernel paging request at virtual address 1a480000 pgd
> > = 80004000 [1a480000] *pgd=00000000 Internal error: Oops: 805 [#1] SMP
> > ARM
> 
> [...]
> 
> > The kernel panic is caused by the sg_buf is not set correctly with the
> > following code when compiled with Yocto GCC 4.8.1:
> >
> > drivers/net/wireless/ath/ath6kl/hif.h:
> > struct hif_scatter_req {
> >         struct list_head list;
> >         /* address for the read/write operation */
> >         u32 addr;
> > 	...
> >
> >         /* bounce buffer for upper layers to copy to/from */
> >         u8 *virt_dma_buf;
> >
> >         struct hif_scatter_item scat_list[1];
> >
> >         u32 scat_q_depth;
> > };
> >
> > (Note: the scat_req.scat_list[] will dynamiclly grow with run-time)
> 
> There's actually a major bug right there, scat_list can corrupt
> scat_q_depth.
> 
> > The GCC 4.8.1 compiler will not do the for-loop till scat_entries,
> > instead, it only run one round loop. This may be caused by that the
> > GCC 4.8.1 thought that the scat_list only have one item and then no
> > need to do full iteration, but this is simply wrong by looking at the
> > assebly code. This will cause the sg buffer not get set when
> scat_entries > 1 and thus lead to kernel panic.
> >
> > This patch is a workaround to the GCC 4.8.1 complier issue by passing
> > the entry address of the scat_req->scat_list to the for-loop and
> > interate it, then, GCC 4.8.1 will do the full for-loop correctly.
> > (Note: This issue not observed with GCC 4.7.2, only found on the GCC
> > 4.8.1)
> >
> > This patch does not change any function logic and no any performance
> downgrade.
> 
> [...]
> 
> > +	scat_list = &scat_req->scat_list[0];
> > +
> >  	/* assemble SG list */
> > -	for (i = 0; i < scat_req->scat_entries; i++, sg++) {
> > +	for (i = 0; i < scat_req->scat_entries; i++, sg++, scat_list++) {
> >  		ath6kl_dbg(ATH6KL_DBG_SCATTER, "%d: addr:0x%p, len:%d\n",
> > -			   i, scat_req->scat_list[i].buf,
> > -			   scat_req->scat_list[i].len);
> > +			   i, scat_list->buf, scat_list->len);
> >
> > -		sg_set_buf(sg, scat_req->scat_list[i].buf,
> > -			   scat_req->scat_list[i].len);
> > +		sg_set_buf(sg, scat_list->buf, scat_list->len);
> >  	}
> 
> Working around the problem by adding a temporary variable makes me a bit
> worried, I would rather fix the root cause. Is the root cause by that we
> define the field with scat_list[1]?

Yes, this is what I assumed. 

> 
> Does the patch below help? It would also fix the corruption with
> scat_q_depth. Please note that I have only compile tested it. And I might
> have also missed something important, so please review it carefully.

Yes, Firstly, I have looked at the asm code and the compiler(gcc 4.8.1) works correctly after applying
the following patch. Secondly, I have tested the patch with compiler(gcc 4.8.1) on the real HW, and it
works fine too. Without the patch, the kernel crash will happen 100%.

Thus, for the patch:

Acked-by: Jason Liu <r64343 at freescale.com>
Tested-by: Jason Liu <r64343 at freescale.com>

Jason Liu

> 
> --- a/drivers/net/wireless/ath/ath6kl/hif.h
> +++ b/drivers/net/wireless/ath/ath6kl/hif.h
> @@ -197,9 +197,9 @@ struct hif_scatter_req {
>  	/* bounce buffer for upper layers to copy to/from */
>  	u8 *virt_dma_buf;
> 
> -	struct hif_scatter_item scat_list[1];
> -
>  	u32 scat_q_depth;
> +
> +	struct hif_scatter_item scat_list[0];
>  };
> 
>  struct ath6kl_irq_proc_registers {
> diff --git a/drivers/net/wireless/ath/ath6kl/sdio.c
> b/drivers/net/wireless/ath/ath6kl/sdio.c
> index 7126bdd..6bf15a3 100644
> --- a/drivers/net/wireless/ath/ath6kl/sdio.c
> +++ b/drivers/net/wireless/ath/ath6kl/sdio.c
> @@ -348,7 +348,7 @@ static int ath6kl_sdio_alloc_prep_scat_req(struct
> ath6kl_sdio *ar_sdio,
>  	int i, scat_req_sz, scat_list_sz, size;
>  	u8 *virt_buf;
> 
> -	scat_list_sz = (n_scat_entry - 1) * sizeof(struct hif_scatter_item);
> +	scat_list_sz = n_scat_entry * sizeof(struct hif_scatter_item);
>  	scat_req_sz = sizeof(*s_req) + scat_list_sz;
> 
>  	if (!virt_scat)
> 
> 
> --
> Kalle Valo