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Commit 8c9c2bf7 authored by Arne Jansen's avatar Arne Jansen Committed by David Sterba
Browse files

btrfs: fix race in reada 



When inserting into the radix tree returns EEXIST, get the existing
entry without giving up the spinlock in between.
There was a race for both the zones trees and the extent tree.

Signed-off-by: default avatarArne Jansen <sensille@gmx.net>
parent 848cce0d

fs/btrfs/inode.c

+7 −1
Original line number Diff line number Diff line
@@ -4332,7 +4332,13 @@ static int btrfs_real_readdir(struct file *filp, void *dirent, 
			}

no_dentry:

			/* is this a reference to our own snapshot? If so

			 * skip it

			 * skip it.

			 *

			 * In contrast to old kernels, we insert the snapshot's

			 * dir item and dir index after it has been created, so

			 * we won't find a reference to our own snapshot. We

			 * still keep the following code for backward

			 * compatibility.

			 */

			if (location.type == BTRFS_ROOT_ITEM_KEY &&

			    location.objectid == root->root_key.objectid) {

fs/btrfs/reada.c

+16 −19
Original line number Diff line number Diff line
@@ -250,14 +250,12 @@ static struct reada_zone *reada_find_zone(struct btrfs_fs_info *fs_info, 
					  struct btrfs_bio *bbio)

{

	int ret;

	int looped = 0;

	struct reada_zone *zone;

	struct btrfs_block_group_cache *cache = NULL;

	u64 start;

	u64 end;

	int i;



again:

	zone = NULL;

	spin_lock(&fs_info->reada_lock);

	ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,
@@ -274,9 +272,6 @@ again: 
		spin_unlock(&fs_info->reada_lock);

	}



	if (looped)

		return NULL;



	cache = btrfs_lookup_block_group(fs_info, logical);

	if (!cache)

		return NULL;
@@ -307,13 +302,15 @@ again: 
	ret = radix_tree_insert(&dev->reada_zones,

				(unsigned long)(zone->end >> PAGE_CACHE_SHIFT),

				zone);

	spin_unlock(&fs_info->reada_lock);



	if (ret) {

	if (ret == -EEXIST) {

		kfree(zone);

		looped = 1;

		goto again;

		ret = radix_tree_gang_lookup(&dev->reada_zones, (void **)&zone,

					     logical >> PAGE_CACHE_SHIFT, 1);

		if (ret == 1)

			kref_get(&zone->refcnt);

	}

	spin_unlock(&fs_info->reada_lock);



	return zone;

}
@@ -323,8 +320,8 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root, 
					      struct btrfs_key *top, int level)

{

	int ret;

	int looped = 0;

	struct reada_extent *re = NULL;

	struct reada_extent *re_exist = NULL;

	struct btrfs_fs_info *fs_info = root->fs_info;

	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;

	struct btrfs_bio *bbio = NULL;
@@ -335,14 +332,13 @@ static struct reada_extent *reada_find_extent(struct btrfs_root *root, 
	int i;

	unsigned long index = logical >> PAGE_CACHE_SHIFT;



again:

	spin_lock(&fs_info->reada_lock);

	re = radix_tree_lookup(&fs_info->reada_tree, index);

	if (re)

		kref_get(&re->refcnt);

	spin_unlock(&fs_info->reada_lock);



	if (re || looped)

	if (re)

		return re;



	re = kzalloc(sizeof(*re), GFP_NOFS);
@@ -398,12 +394,15 @@ again: 
	/* insert extent in reada_tree + all per-device trees, all or nothing */

	spin_lock(&fs_info->reada_lock);

	ret = radix_tree_insert(&fs_info->reada_tree, index, re);

	if (ret) {

	if (ret == -EEXIST) {

		re_exist = radix_tree_lookup(&fs_info->reada_tree, index);

		BUG_ON(!re_exist);

		kref_get(&re_exist->refcnt);

		spin_unlock(&fs_info->reada_lock);

		if (ret != -ENOMEM) {

			/* someone inserted the extent in the meantime */

			looped = 1;

		goto error;

	}

	if (ret) {

		spin_unlock(&fs_info->reada_lock);

		goto error;

	}

	for (i = 0; i < nzones; ++i) {
@@ -450,9 +449,7 @@ error: 
	}

	kfree(bbio);

	kfree(re);

	if (looped)

		goto again;

	return NULL;

	return re_exist;

}



static void reada_kref_dummy(struct kref *kr)