[Xen-devel] [PATCH] xen/pciback: Use mutexes when working with Xenbus state transitions.

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

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
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@xxxxxxxxxx>
---
 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;
 }
 
-- 
1.7.4.1


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel