[Xen-devel] [PATCH] gntdev: switch back to rwlocks

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi Jeremy,
this patch switches back from spinlocks to rwlocks in gntdev, solving
the locking issue that was preventing stubdoms from working.
In particular the problem is that gntdev_mmap calls apply_to_page_range
after acquiring the spinlock. apply_to_page_range causes the mmu
notifiers to be called, so mn_invl_range_start will be called that will
try to acquire again the same spinlock.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

---

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index a33e443..0a9a68c 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -51,7 +51,7 @@ struct gntdev_priv {
        struct list_head maps;
        uint32_t used;
        uint32_t limit;
-       spinlock_t lock;
+       rwlock_t rwlock;
        struct mm_struct *mm;
        struct mmu_notifier mn;
 };
@@ -289,7 +289,7 @@ static void mn_invl_range_start(struct mmu_notifier *mn,
        unsigned long mstart, mend;
        int err;
 
-       spin_lock(&priv->lock);
+       read_lock(&priv->rwlock);
        list_for_each_entry(map, &priv->maps, next) {
                if (!map->vma)
                        continue;
@@ -311,7 +311,7 @@ static void mn_invl_range_start(struct mmu_notifier *mn,
                                        (mend - mstart) >> PAGE_SHIFT);
                WARN_ON(err);
        }
-       spin_unlock(&priv->lock);
+       read_unlock(&priv->rwlock);
 }
 
 static void mn_invl_page(struct mmu_notifier *mn,
@@ -328,7 +328,7 @@ static void mn_release(struct mmu_notifier *mn,
        struct grant_map *map;
        int err;
 
-       spin_lock(&priv->lock);
+       read_lock(&priv->rwlock);
        list_for_each_entry(map, &priv->maps, next) {
                if (!map->vma)
                        continue;
@@ -339,7 +339,7 @@ static void mn_release(struct mmu_notifier *mn,
                err = unmap_grant_pages(map, 0, map->count);
                WARN_ON(err);
        }
-       spin_unlock(&priv->lock);
+       read_unlock(&priv->rwlock);
 }
 
 struct mmu_notifier_ops gntdev_mmu_ops = {
@@ -359,7 +359,7 @@ static int gntdev_open(struct inode *inode, struct file 
*flip)
                return -ENOMEM;
 
        INIT_LIST_HEAD(&priv->maps);
-       spin_lock_init(&priv->lock);
+       priv->rwlock = RW_LOCK_UNLOCKED;
        priv->limit = limit;
 
        priv->mm = get_task_mm(current);
@@ -387,7 +387,7 @@ static int gntdev_release(struct inode *inode, struct file 
*flip)
        if (debug)
                printk("%s: priv %p\n", __FUNCTION__, priv);
 
-       spin_lock(&priv->lock);
+       write_lock(&priv->rwlock);
        while (!list_empty(&priv->maps)) {
                map = list_entry(priv->maps.next, struct grant_map, next);
                err = gntdev_del_map(map);
@@ -395,7 +395,7 @@ static int gntdev_release(struct inode *inode, struct file 
*flip)
                        gntdev_free_map(map);
 
        }
-       spin_unlock(&priv->lock);
+       write_unlock(&priv->rwlock);
 
        mmu_notifier_unregister(&priv->mn, priv->mm);
        kfree(priv);
@@ -429,15 +429,15 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv 
*priv,
                return err;
        }
 
-       spin_lock(&priv->lock);
+       write_lock(&priv->rwlock);
        gntdev_add_map(priv, map);
        op.index = map->index << PAGE_SHIFT;
-       spin_unlock(&priv->lock);
+       write_unlock(&priv->rwlock);
 
        if (copy_to_user(u, &op, sizeof(op)) != 0) {
-               spin_lock(&priv->lock);
+               write_lock(&priv->rwlock);
                gntdev_del_map(map);
-               spin_unlock(&priv->lock);
+               write_unlock(&priv->rwlock);
                gntdev_free_map(map);
                return err;
        }
@@ -457,11 +457,11 @@ static long gntdev_ioctl_unmap_grant_ref(struct 
gntdev_priv *priv,
                printk("%s: priv %p, del %d+%d\n", __FUNCTION__, priv,
                       (int)op.index, (int)op.count);
 
-       spin_lock(&priv->lock);
+       write_lock(&priv->rwlock);
        map = gntdev_find_map_index(priv, op.index >> PAGE_SHIFT, op.count);
        if (map)
                err = gntdev_del_map(map);
-       spin_unlock(&priv->lock);
+       write_unlock(&priv->rwlock);
        if (!err)
                gntdev_free_map(map);
        return err;
@@ -479,16 +479,16 @@ static long gntdev_ioctl_get_offset_for_vaddr(struct 
gntdev_priv *priv,
                printk("%s: priv %p, offset for vaddr %lx\n", __FUNCTION__, 
priv,
                       (unsigned long)op.vaddr);
 
-       spin_lock(&priv->lock);
+       read_lock(&priv->rwlock);
        map = gntdev_find_map_vaddr(priv, op.vaddr);
        if (map == NULL ||
            map->vma->vm_start != op.vaddr) {
-               spin_unlock(&priv->lock);
+               read_unlock(&priv->rwlock);
                return -EINVAL;
        }
        op.offset = map->index << PAGE_SHIFT;
        op.count = map->count;
-       spin_unlock(&priv->lock);
+       read_unlock(&priv->rwlock);
 
        if (copy_to_user(u, &op, sizeof(op)) != 0)
                return -EFAULT;
@@ -507,9 +507,9 @@ static long gntdev_ioctl_set_max_grants(struct gntdev_priv 
*priv,
        if (op.count > limit)
                return -EINVAL;
 
-       spin_lock(&priv->lock);
+       write_lock(&priv->rwlock);
        priv->limit = op.count;
-       spin_unlock(&priv->lock);
+       write_unlock(&priv->rwlock);
        return 0;
 }
 
@@ -557,7 +557,7 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
                printk("%s: map %d+%d at %lx (pgoff %lx)\n", __FUNCTION__,
                       index, count, vma->vm_start, vma->vm_pgoff);
 
-       spin_lock(&priv->lock);
+       read_lock(&priv->rwlock);
        map = gntdev_find_map_index(priv, index, count);
        if (!map)
                goto unlock_out;
@@ -599,7 +599,7 @@ static int gntdev_mmap(struct file *flip, struct 
vm_area_struct *vma)
        map->is_mapped = 1;
 
 unlock_out:
-       spin_unlock(&priv->lock);
+       read_unlock(&priv->rwlock);
        return err;
 }
 

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