[Xen-devel] [PATCH] xen/pciback: use mutex rather than spinlock in passthrough backend

["Jan Beulich" <JBeulich@xxxxxxxx>]

To accommodate the call to the callback function from
__xen_pcibk_publish_pci_roots(), which so far dropped and the re-
acquired the lock without checking that the list didn't actually
change, convert the code to use a mutex instead (observing that the
code taking the lock won't ever get called from non-sleepable
context).

As a result, drop the bogus use of list_for_each_entry_safe() and
remove the inappropriate dropping of the lock.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

---
 drivers/xen/xen-pciback/passthrough.c |   32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

--- 3.1-rc6/drivers/xen/xen-pciback/passthrough.c
+++ 3.1-rc6-xen-pciback-passthr-mutex/drivers/xen/xen-pciback/passthrough.c
@@ -7,13 +7,13 @@
 
 #include <linux/list.h>
 #include <linux/pci.h>
-#include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include "pciback.h"
 
 struct passthrough_dev_data {
        /* Access to dev_list must be protected by lock */
        struct list_head dev_list;
-       spinlock_t lock;
+       struct mutex lock;
 };
 
 static struct pci_dev *__xen_pcibk_get_pci_dev(struct xen_pcibk_device *pdev,
@@ -24,9 +24,8 @@ static struct pci_dev *__xen_pcibk_get_p
        struct passthrough_dev_data *dev_data = pdev->pci_dev_data;
        struct pci_dev_entry *dev_entry;
        struct pci_dev *dev = NULL;
-       unsigned long flags;
 
-       spin_lock_irqsave(&dev_data->lock, flags);
+       mutex_lock(&dev_data->lock);
 
        list_for_each_entry(dev_entry, &dev_data->dev_list, list) {
                if (domain == (unsigned int)pci_domain_nr(dev_entry->dev->bus)
@@ -37,7 +36,7 @@ static struct pci_dev *__xen_pcibk_get_p
                }
        }
 
-       spin_unlock_irqrestore(&dev_data->lock, flags);
+       mutex_unlock(&dev_data->lock);
 
        return dev;
 }
@@ -48,7 +47,6 @@ static int __xen_pcibk_add_pci_dev(struc
 {
        struct passthrough_dev_data *dev_data = pdev->pci_dev_data;
        struct pci_dev_entry *dev_entry;
-       unsigned long flags;
        unsigned int domain, bus, devfn;
        int err;
 
@@ -57,9 +55,9 @@ static int __xen_pcibk_add_pci_dev(struc
                return -ENOMEM;
        dev_entry->dev = dev;
 
-       spin_lock_irqsave(&dev_data->lock, flags);
+       mutex_lock(&dev_data->lock);
        list_add_tail(&dev_entry->list, &dev_data->dev_list);
-       spin_unlock_irqrestore(&dev_data->lock, flags);
+       mutex_unlock(&dev_data->lock);
 
        /* Publish this device. */
        domain = (unsigned int)pci_domain_nr(dev->bus);
@@ -76,9 +74,8 @@ static void __xen_pcibk_release_pci_dev(
        struct passthrough_dev_data *dev_data = pdev->pci_dev_data;
        struct pci_dev_entry *dev_entry, *t;
        struct pci_dev *found_dev = NULL;
-       unsigned long flags;
 
-       spin_lock_irqsave(&dev_data->lock, flags);
+       mutex_lock(&dev_data->lock);
 
        list_for_each_entry_safe(dev_entry, t, &dev_data->dev_list, list) {
                if (dev_entry->dev == dev) {
@@ -88,7 +85,7 @@ static void __xen_pcibk_release_pci_dev(
                }
        }
 
-       spin_unlock_irqrestore(&dev_data->lock, flags);
+       mutex_unlock(&dev_data->lock);
 
        if (found_dev)
                pcistub_put_pci_dev(found_dev);
@@ -102,7 +99,7 @@ static int __xen_pcibk_init_devices(stru
        if (!dev_data)
                return -ENOMEM;
 
-       spin_lock_init(&dev_data->lock);
+       mutex_init(&dev_data->lock);
 
        INIT_LIST_HEAD(&dev_data->dev_list);
 
@@ -116,14 +113,14 @@ static int __xen_pcibk_publish_pci_roots
 {
        int err = 0;
        struct passthrough_dev_data *dev_data = pdev->pci_dev_data;
-       struct pci_dev_entry *dev_entry, *e, *tmp;
+       struct pci_dev_entry *dev_entry, *e;
        struct pci_dev *dev;
        int found;
        unsigned int domain, bus;
 
-       spin_lock(&dev_data->lock);
+       mutex_lock(&dev_data->lock);
 
-       list_for_each_entry_safe(dev_entry, tmp, &dev_data->dev_list, list) {
+       list_for_each_entry(dev_entry, &dev_data->dev_list, list) {
                /* Only publish this device as a root if none of its
                 * parent bridges are exported
                 */
@@ -142,16 +139,13 @@ static int __xen_pcibk_publish_pci_roots
                bus = (unsigned int)dev_entry->dev->bus->number;
 
                if (!found) {
-                       spin_unlock(&dev_data->lock);
                        err = publish_root_cb(pdev, domain, bus);
                        if (err)
                                break;
-                       spin_lock(&dev_data->lock);
                }
        }
 
-       if (!err)
-               spin_unlock(&dev_data->lock);
+       mutex_unlock(&dev_data->lock);
 
        return err;
 }



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