linux-kernel - Re: [PATCH 2/2] dmaengine: qcom_hidma: assign channel cookie correctly

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Date:   Fri, 4 Jan 2019 23:01:11 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Shunyong Yang <shunyong.yang@...-semitech.com>
Cc:     okaya@...nel.org, andy.gross@...aro.org, david.brown@...aro.org,
        dan.j.williams@...el.com, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Joey Zheng <yu.zheng@...-semitech.com>
Subject: Re: [PATCH 2/2] dmaengine: qcom_hidma: assign channel cookie
 correctly

On 07-12-18, 12:29, Shunyong Yang wrote:
> When dma_cookie_complete() is called in hidma_process_completed(),
> dma_cookie_status() will return DMA_COMPLETE in hidma_tx_status(). Then,
> hidma_txn_is_success() will be called to use channel cookie
> mchan->last_success to do additional DMA status check. Current code
> assigns mchan->last_success after dma_cookie_complete(). This causes
> a race condition of dma_cookie_status() returns DMA_COMPLETE before
> mchan->last_success is assigned correctly. The race will cause
> hidma_tx_status() return DMA_ERROR but the transaction is actually a
> success. Moreover, in async_tx case, it will cause a timeout panic
> in async_tx_quiesce().
> 
>  Kernel panic - not syncing: async_tx_quiesce: DMA error waiting for
>  transaction
>  ...
>  Call trace:
>  [<ffff000008089994>] dump_backtrace+0x0/0x1f4
>  [<ffff000008089bac>] show_stack+0x24/0x2c
>  [<ffff00000891e198>] dump_stack+0x84/0xa8
>  [<ffff0000080da544>] panic+0x12c/0x29c
>  [<ffff0000045d0334>] async_tx_quiesce+0xa4/0xc8 [async_tx]
>  [<ffff0000045d03c8>] async_trigger_callback+0x70/0x1c0 [async_tx]
>  [<ffff0000048b7d74>] raid_run_ops+0x86c/0x1540 [raid456]
>  [<ffff0000048bd084>] handle_stripe+0x5e8/0x1c7c [raid456]
>  [<ffff0000048be9ec>] handle_active_stripes.isra.45+0x2d4/0x550 [raid456]
>  [<ffff0000048beff4>] raid5d+0x38c/0x5d0 [raid456]
>  [<ffff000008736538>] md_thread+0x108/0x168
>  [<ffff0000080fb1cc>] kthread+0x10c/0x138
>  [<ffff000008084d34>] ret_from_fork+0x10/0x18
> 
> Cc: Joey Zheng <yu.zheng@...-semitech.com>
> Signed-off-by: Shunyong Yang <shunyong.yang@...-semitech.com>
> ---
>  drivers/dma/qcom/hidma.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/qcom/hidma.c b/drivers/dma/qcom/hidma.c
> index 9d639ed1955a..aa88bcceda20 100644
> --- a/drivers/dma/qcom/hidma.c
> +++ b/drivers/dma/qcom/hidma.c
> @@ -138,24 +138,24 @@ static void hidma_process_completed(struct hidma_chan *mchan)
>  		desc = &mdesc->desc;
>  		last_cookie = desc->cookie;
>  
> +		llstat = hidma_ll_status(mdma->lldev, mdesc->tre_ch);
> +
>  		spin_lock_irqsave(&mchan->lock, irqflags);
> +		if (llstat == DMA_COMPLETE) {
> +			mchan->last_success = last_cookie;
> +			result.result = DMA_TRANS_NOERROR;
> +		} else
> +			result.result = DMA_TRANS_ABORTED;

Coding style mandates that else should also have braces, please fix that

-- 
~Vinod