[Xen-devel] [PATCH] xen/xenbus: fix locking

[Juergen Gross <jgross@xxxxxxxx>]

Commit 060eabe8fbe726 ("xenbus/backend: Protect xenbus callback with
lock") introduced a bug by holding a lock while calling a function
which might schedule.

Fix that by using a semaphore instead.

Fixes: 060eabe8fbe726 ("xenbus/backend: Protect xenbus callback with lock")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 drivers/xen/xenbus/xenbus_probe.c         | 10 +++++-----
 drivers/xen/xenbus/xenbus_probe_backend.c |  5 +++--
 include/xen/xenbus.h                      |  3 ++-
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe.c 
b/drivers/xen/xenbus/xenbus_probe.c
index 66975da4f3b6..8c4d05b687b7 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -239,9 +239,9 @@ int xenbus_dev_probe(struct device *_dev)
                goto fail;
        }
 
-       spin_lock(&dev->reclaim_lock);
+       down(&dev->reclaim_sem);
        err = drv->probe(dev, id);
-       spin_unlock(&dev->reclaim_lock);
+       up(&dev->reclaim_sem);
        if (err)
                goto fail_put;
 
@@ -271,9 +271,9 @@ int xenbus_dev_remove(struct device *_dev)
        free_otherend_watch(dev);
 
        if (drv->remove) {
-               spin_lock(&dev->reclaim_lock);
+               down(&dev->reclaim_sem);
                drv->remove(dev);
-               spin_unlock(&dev->reclaim_lock);
+               up(&dev->reclaim_sem);
        }
 
        module_put(drv->driver.owner);
@@ -473,7 +473,7 @@ int xenbus_probe_node(struct xen_bus_type *bus,
                goto fail;
 
        dev_set_name(&xendev->dev, "%s", devname);
-       spin_lock_init(&xendev->reclaim_lock);
+       sema_init(&xendev->reclaim_sem, 1);
 
        /* Register with generic device framework. */
        err = device_register(&xendev->dev);
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c 
b/drivers/xen/xenbus/xenbus_probe_backend.c
index 791f6fe01e91..9b2fbe69bccc 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -45,6 +45,7 @@
 #include <linux/mm.h>
 #include <linux/notifier.h>
 #include <linux/export.h>
+#include <linux/semaphore.h>
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
@@ -257,10 +258,10 @@ static int backend_reclaim_memory(struct device *dev, 
void *data)
        drv = to_xenbus_driver(dev->driver);
        if (drv && drv->reclaim_memory) {
                xdev = to_xenbus_device(dev);
-               if (!spin_trylock(&xdev->reclaim_lock))
+               if (down_trylock(&xdev->reclaim_sem))
                        return 0;
                drv->reclaim_memory(xdev);
-               spin_unlock(&xdev->reclaim_lock);
+               up(&xdev->reclaim_sem);
        }
        return 0;
 }
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 89a889585ba0..850a43bd69d3 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -42,6 +42,7 @@
 #include <linux/completion.h>
 #include <linux/init.h>
 #include <linux/slab.h>
+#include <linux/semaphore.h>
 #include <xen/interface/xen.h>
 #include <xen/interface/grant_table.h>
 #include <xen/interface/io/xenbus.h>
@@ -76,7 +77,7 @@ struct xenbus_device {
        enum xenbus_state state;
        struct completion down;
        struct work_struct work;
-       spinlock_t reclaim_lock;
+       struct semaphore reclaim_sem;
 };
 
 static inline struct xenbus_device *to_xenbus_device(struct device *dev)
-- 
2.16.4


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