Re: [Xen-devel] [PATCH] xen/mce: schedule a workqueue to avoid sleep in atomic context

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Jun 12, 2012 at 07:51:03AM +0000, Liu, Jinsong wrote:
> >From aa2ce7440f16002266dc8464f749992d0c8ac0e5 Mon Sep 17 00:00:00 2001
> From: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
> Date: Tue, 12 Jun 2012 23:11:16 +0800
> Subject: [PATCH] xen/mce: schedule a workqueue to avoid sleep in atomic 
> context
> 
> copy_to_user might sleep and print a stack trace if it is executed
> in an atomic spinlock context.
> 
> This patch schedule a workqueue for IRQ handler to poll the data,
> and use mutex instead of spinlock, so copy_to_user sleep in atomic
> context would not occur.

Ah much better. Usually one also includes the report of what the
stack trace was. So I've added that in.

> 
> Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Suggested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Signed-off-by: Liu, Jinsong <jinsong.liu@xxxxxxxxx>
> ---
>  drivers/xen/mcelog.c |   18 +++++++++++-------
>  1 files changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/xen/mcelog.c b/drivers/xen/mcelog.c
> index 72e87d2..804aa3c 100644
> --- a/drivers/xen/mcelog.c
> +++ b/drivers/xen/mcelog.c
> @@ -55,7 +55,7 @@ static struct mc_info g_mi;
>  static struct mcinfo_logical_cpu *g_physinfo;
>  static uint32_t ncpus;
>  
> -static DEFINE_SPINLOCK(mcelog_lock);
> +static DEFINE_MUTEX(mcelog_lock);
>  
>  static struct xen_mce_log xen_mcelog = {
>       .signature      = XEN_MCE_LOG_SIGNATURE,
> @@ -106,7 +106,7 @@ static ssize_t xen_mce_chrdev_read(struct file *filp, 
> char __user *ubuf,
>       unsigned num;
>       int i, err;
>  
> -     spin_lock(&mcelog_lock);
> +     mutex_lock(&mcelog_lock);
>  
>       num = xen_mcelog.next;
>  
> @@ -130,7 +130,7 @@ static ssize_t xen_mce_chrdev_read(struct file *filp, 
> char __user *ubuf,
>               err = -EFAULT;
>  
>  out:
> -     spin_unlock(&mcelog_lock);
> +     mutex_unlock(&mcelog_lock);
>  
>       return err ? err : buf - ubuf;
>  }
> @@ -310,12 +310,11 @@ static int mc_queue_handle(uint32_t flags)
>  }
>  
>  /* virq handler for machine check error info*/
> -static irqreturn_t xen_mce_interrupt(int irq, void *dev_id)
> +static void xen_mce_work_fn(struct work_struct *work)
>  {
>       int err;
> -     unsigned long tmp;
>  
> -     spin_lock_irqsave(&mcelog_lock, tmp);
> +     mutex_lock(&mcelog_lock);
>  
>       /* urgent mc_info */
>       err = mc_queue_handle(XEN_MC_URGENT);
> @@ -330,8 +329,13 @@ static irqreturn_t xen_mce_interrupt(int irq, void 
> *dev_id)
>               pr_err(XEN_MCELOG
>                      "Failed to handle nonurgent mc_info queue.\n");
>  
> -     spin_unlock_irqrestore(&mcelog_lock, tmp);
> +     mutex_unlock(&mcelog_lock);
> +}
> +static DECLARE_WORK(xen_mce_work, xen_mce_work_fn);
>  
> +static irqreturn_t xen_mce_interrupt(int irq, void *dev_id)
> +{
> +     schedule_work(&xen_mce_work);
>       return IRQ_HANDLED;
>  }
>  
> -- 
> 1.7.1


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