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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: Arne Jansen <sensille@gmx.net>
This commit is contained in:
Arne Jansen 2012-02-25 09:09:30 +01:00 committed by David Sterba
parent 848cce0d41
commit 8c9c2bf7a3
2 changed files with 23 additions and 20 deletions
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8
fs/btrfs/inode.c
View File

@ -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) {

35
fs/btrfs/reada.c
View File

@ -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 == -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);
goto error;
}
if (ret) {
spin_unlock(&fs_info->reada_lock);
if (ret != -ENOMEM) {
/* someone inserted the extent in the meantime */
looped = 1;
}
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)