linux-kernel - Re: [PATCH] xen/pciback: Use mutexes when working with Xenbus state transitions.

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Message-Id: <4E7738E90200007800056A54@nat28.tlf.novell.com>
Date:	Mon, 19 Sep 2011 11:43:21 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Konrad Rzeszutek Wilk" <konrad.wilk@...cle.com>
Cc:	<xen-devel@...ts.xensource.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen/pciback: Use mutexes when working with Xenbus
	 state transitions.

>>> On 16.09.11 at 21:06, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> wrote:

> The caller that orchestrates the state changes is xenwatch_thread
> and it takes a mutex. In our processing of Xenbus states we can take
> the luxery of going to sleep on a mutex, so lets do that and

This is only the direct conversion of existing spinlock accesses in
xenbus.c. However, in the course of converting from the legacy
implementation you stripped a couple more (in xen_pcibk_attach(),
xen_pcibk_reconfigure(), and xen_pcibk_setup_backend()), and
those should now get re-added imo.

Jan

> also fix this bug:
> 
> BUG: sleeping function called from invalid context at 
> /linux/kernel/mutex.c:271
> in_atomic(): 1, irqs_disabled(): 0, pid: 32, name: xenwatch
> 2 locks held by xenwatch/32:
>  #0:  (xenwatch_mutex){......}, at: [<ffffffff813856ab>] 
> xenwatch_thread+0x4b/0x180
>  #1:  (&(&pdev->dev_lock)->rlock){......}, at: [<ffffffff8138f05b>] 
> xen_pcibk_disconnect+0x1b/0x80
> Pid: 32, comm: xenwatch Not tainted 3.1.0-rc6-00015-g3ce340d #2
> Call Trace:
>  [<ffffffff810892b2>] __might_sleep+0x102/0x130
>  [<ffffffff8163b90f>] mutex_lock_nested+0x2f/0x50
>  [<ffffffff81382c1c>] unbind_from_irq+0x2c/0x1b0
>  [<ffffffff8110da66>] ? free_irq+0x56/0xb0
>  [<ffffffff81382dbc>] unbind_from_irqhandler+0x1c/0x30
>  [<ffffffff8138f06b>] xen_pcibk_disconnect+0x2b/0x80
>  [<ffffffff81390348>] xen_pcibk_frontend_changed+0xe8/0x140
>  [<ffffffff81387ac2>] xenbus_otherend_changed+0xd2/0x150
>  [<ffffffff810895c1>] ? get_parent_ip+0x11/0x50
>  [<ffffffff81387de0>] frontend_changed+0x10/0x20
>  [<ffffffff81385712>] xenwatch_thread+0xb2/0x180
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  drivers/xen/xen-pciback/pciback.h |    2 +-
>  drivers/xen/xen-pciback/xenbus.c  |   16 +++++-----------
>  2 files changed, 6 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/xen/xen-pciback/pciback.h 
> b/drivers/xen/xen-pciback/pciback.h
> index a0e131a..c3af628 100644
> --- a/drivers/xen/xen-pciback/pciback.h
> +++ b/drivers/xen/xen-pciback/pciback.h
> @@ -27,7 +27,7 @@ struct pci_dev_entry {
>  
>  struct xen_pcibk_device {
>  	void *pci_dev_data;
> -	spinlock_t dev_lock;
> +	struct mutex dev_lock;
>  	struct xenbus_device *xdev;
>  	struct xenbus_watch be_watch;
>  	u8 be_watching;
> diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
> index 978d2c6..c057d67 100644
> --- a/drivers/xen/xen-pciback/xenbus.c
> +++ b/drivers/xen/xen-pciback/xenbus.c
> @@ -44,7 +44,7 @@ static struct xen_pcibk_device *alloc_pdev(struct 
> xenbus_device *xdev)
>  	pdev->xdev = xdev;
>  	dev_set_drvdata(&xdev->dev, pdev);
>  
> -	spin_lock_init(&pdev->dev_lock);
> +	mutex_init(&pdev->dev_lock);
>  
>  	pdev->sh_info = NULL;
>  	pdev->evtchn_irq = INVALID_EVTCHN_IRQ;
> @@ -62,14 +62,13 @@ out:
>  
>  static void xen_pcibk_disconnect(struct xen_pcibk_device *pdev)
>  {
> -	spin_lock(&pdev->dev_lock);
> +	mutex_lock(&pdev->dev_lock);
>  
>  	/* Ensure the guest can't trigger our handler before removing devices */
>  	if (pdev->evtchn_irq != INVALID_EVTCHN_IRQ) {
>  		unbind_from_irqhandler(pdev->evtchn_irq, pdev);
>  		pdev->evtchn_irq = INVALID_EVTCHN_IRQ;
>  	}
> -	spin_unlock(&pdev->dev_lock);
>  
>  	/* If the driver domain started an op, make sure we complete it
>  	 * before releasing the shared memory */
> @@ -77,13 +76,11 @@ static void xen_pcibk_disconnect(struct xen_pcibk_device 
> *pdev)
>  	/* Note, the workqueue does not use spinlocks at all.*/
>  	flush_workqueue(xen_pcibk_wq);
>  
> -	spin_lock(&pdev->dev_lock);
>  	if (pdev->sh_info != NULL) {
>  		xenbus_unmap_ring_vfree(pdev->xdev, pdev->sh_info);
>  		pdev->sh_info = NULL;
>  	}
> -	spin_unlock(&pdev->dev_lock);
> -
> +	mutex_unlock(&pdev->dev_lock);
>  }
>  
>  static void free_pdev(struct xen_pcibk_device *pdev)
> @@ -120,9 +117,8 @@ static int xen_pcibk_do_attach(struct xen_pcibk_device 
> *pdev, int gnt_ref,
>  		goto out;
>  	}
>  
> -	spin_lock(&pdev->dev_lock);
> +	mutex_lock(&pdev->dev_lock);
>  	pdev->sh_info = vaddr;
> -	spin_unlock(&pdev->dev_lock);
>  
>  	err = bind_interdomain_evtchn_to_irqhandler(
>  		pdev->xdev->otherend_id, remote_evtchn, xen_pcibk_handle_event,
> @@ -132,14 +128,12 @@ static int xen_pcibk_do_attach(struct xen_pcibk_device 
> *pdev, int gnt_ref,
>  				 "Error binding event channel to IRQ");
>  		goto out;
>  	}
> -
> -	spin_lock(&pdev->dev_lock);
>  	pdev->evtchn_irq = err;
> -	spin_unlock(&pdev->dev_lock);
>  	err = 0;
>  
>  	dev_dbg(&pdev->xdev->dev, "Attached!\n");
>  out:
> +	mutex_unlock(&pdev->dev_lock);
>  	return err;
>  }
>  



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