Re: [PATCH] i2c_dw: deadlock happening when system is trying tosuspend

[Wolfram Sang]

On Tue, Jun 26, 2012 at 02:29:13PM +0000, Liu, Chuansheng wrote:
> From: liu chuansheng <chuansheng.liu@xxxxxxxxx>
> Subject: [PATCH] i2c_dw: deadlock happening when system is trying to suspend
> 
> In i2c_dw code, there is a race condition that causes pm suspend
> thread blocking there always. The scenerio is as below:
> 
> PM thread:
> suspend -->
> pm_suspend -->
> enter_state -->
> dpm_suspend_start(will call i2c_dw_pci_suspend(),
> and the dw_i2c_dev->lock is hold)
> ...
> suspend_enter -->
> dpm_suspend_noirq -->
> suspend_device_irqs -->
> synchronize_irq()
> 
> synchronize_irq will wait for any pending irq is handled, and
> the correpsonding irq thread is finished.
> 
> In this case, there is a i2c device interrupt is pending, the irq
> thread do the below things:
> IRQ thread:
> i2c_smbus_read_byte_data -->
> i2c_smbus_xfer -->
> i2c_transfer -->
> i2c_dw_xfer -->
> down()
> 
> The irq thread blocked at down dw_i2c_dev->lock, because in PM thread,
> it has been hold after calling i2c_dw_pci_suspend(), but PM thread is
> waiting for IRQ thread, then deadlock happened.
> 
> The solution is moving the down() action after pm_runtime_get_sync().
> 
> Signed-off-by: liu chuansheng <chuansheng.liu@xxxxxxxxx>
> ---
>  drivers/i2c/busses/i2c-designware-core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index 1e48bec..748ecb1 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -512,8 +512,8 @@ i2c_dw_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
>  
>         dev_dbg(dev->dev, "%s: msgs: %d\n", __func__, num);
>  
> -       mutex_lock(&dev->lock);
>         pm_runtime_get_sync(dev->dev);
> +       mutex_lock(&dev->lock);
>  
>         INIT_COMPLETION(dev->cmd_complete);
>         dev->msgs = msgs;

Don't you need to place the mutex_unlock() before pm_runtime_put then?

Thanks,

   Wolfram

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Pengutronix e.K.                           | Wolfram Sang                |
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