linux-kernel - Re: [PATCH] dma: pl330: ensure DMA descriptors are zero-initialised

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Message-ID: <CABb+yY1WQ1dJGQe8kK_R0B8A-aCf7OX3WN_dC5k10F3pa=hwVA@mail.gmail.com>
Date:	Fri, 29 Nov 2013 20:48:20 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	dmaengine@...r.kernel.org, Vinod Koul <vinod.koul@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jassi Brar <jaswinder.singh@...aro.org>,
	Dan Williams <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] dma: pl330: ensure DMA descriptors are zero-initialised

Hi Will,

On Fri, Nov 29, 2013 at 5:20 PM, Will Deacon <will.deacon@....com> wrote:
>
> I see the following splat with 3.13-rc1 when attempting to perform DMA:
>
> [  253.004516] Alignment trap: not handling instruction e1902f9f at [<c0204b40>]
> [  253.004583] Unhandled fault: alignment exception (0x221) at 0xdfdfdfd7
> [  253.004646] Internal error: : 221 [#1] PREEMPT SMP ARM
> [  253.004691] Modules linked in: dmatest(+) [last unloaded: dmatest]
> [  253.004798] CPU: 0 PID: 671 Comm: kthreadd Not tainted 3.13.0-rc1+ #2
> [  253.004864] task: df9b0900 ti: df03e000 task.ti: df03e000
> [  253.004937] PC is at dmaengine_unmap_put+0x14/0x34
> [  253.005010] LR is at pl330_tasklet+0x3c8/0x550
> [  253.005087] pc : [<c0204b44>]    lr : [<c0207478>]    psr: a00e0193
> [  253.005087] sp : df03fe48  ip : 00000000  fp : df03bf18
> [  253.005178] r10: bf00e108  r9 : 00000001  r8 : 00000000
> [  253.005245] r7 : df837040  r6 : dfb41800  r5 : df837048  r4 : df837000
> [  253.005316] r3 : dfdfdfcf  r2 : dfb41f80  r1 : df837048  r0 : dfdfdfd7
> [  253.005384] Flags: NzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment kernel
> [  253.005459] Control: 30c5387d  Table: 9fb9ba80  DAC: fffffffd
> [  253.005520] Process kthreadd (pid: 671, stack limit = 0xdf03e248)
>
> This is due to desc->txd.unmap containing garbage (uninitialised memory).
>
> Rather than add another dummy initialisation to _init_desc, instead
> ensure that the descriptors are zero-initialised during allocation and
> remove the dummy, per-field initialisation.
>
> Cc: Jassi Brar <jaswinder.singh@...aro.org>
> Cc: Vinod Koul <vinod.koul@...el.com>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Will Deacon <will.deacon@....com>
> ---
>  drivers/dma/pl330.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 98641eaca080..79e52a94f054 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2492,14 +2492,8 @@ static dma_cookie_t pl330_tx_submit(struct dma_async_tx_descriptor *tx)
>
>  static inline void _init_desc(struct dma_pl330_desc *desc)
>  {
> -       desc->pchan = NULL;
>         desc->req.x = &desc->px;
>         desc->req.token = desc;
> -       desc->rqcfg.swap = SWAP_NO;
> -       desc->rqcfg.privileged = 0;
> -       desc->rqcfg.insnaccess = 0;
> -       desc->rqcfg.scctl = SCCTRL0;
> -       desc->rqcfg.dcctl = DCCTRL0;
>
These happen to evaluate to 0, but for completeness sake they ought to
be initialized somewhere. Otherwise we might as well drop these
members.

However I don't strongly feel about either way. So whatever comes in v2...

Acked-by: Jassi Brar <jassisinghbrar@...il.com>
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