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xen/xenbus: fix locking

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Commit 060eabe8fb ("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: 060eabe8fb ("xenbus/backend: Protect xenbus callback with lock")
Signed-off-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20200305100323.16736-1-jgross@suse.com
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
This commit is contained in:
Juergen Gross 2020-03-05 11:03:23 +01:00 committed by Boris Ostrovsky
parent 8130b9d5b5
commit 2f69a110e7
3 changed files with 10 additions and 8 deletions
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10
drivers/xen/xenbus/xenbus_probe.c
View File

@ -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);

5
drivers/xen/xenbus/xenbus_probe_backend.c
View File

@ -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;
}

3
include/xen/xenbus.h
View File

@ -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)