btrfs: do nofs allocations when adding and removing qgroup relations

When adding or removing a qgroup relation we are doing a GFP_KERNEL
allocation which is not safe because we are holding a transaction
handle open and that can make us deadlock if the allocator needs to
recurse into the filesystem. So just surround those calls with a
nofs context.

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index a3f0d20..d690ef7 100644 (file)
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -11,6 +11,7 @@
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 #include <linux/btrfs.h>
+#include <linux/sched/mm.h>
 
 #include "ctree.h"
 #include "transaction.h"
@@ -1324,13 +1325,17 @@ int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src,
        struct btrfs_qgroup *member;
        struct btrfs_qgroup_list *list;
        struct ulist *tmp;
+       unsigned int nofs_flag;
        int ret = 0;
 
        /* Check the level of src and dst first */
        if (btrfs_qgroup_level(src) >= btrfs_qgroup_level(dst))
                return -EINVAL;
 
+       /* We hold a transaction handle open, must do a NOFS allocation. */
+       nofs_flag = memalloc_nofs_save();
        tmp = ulist_alloc(GFP_KERNEL);
+       memalloc_nofs_restore(nofs_flag);
        if (!tmp)
                return -ENOMEM;
 
@@ -1387,10 +1392,14 @@ static int __del_qgroup_relation(struct btrfs_trans_handle *trans, u64 src,
        struct btrfs_qgroup_list *list;
        struct ulist *tmp;
        bool found = false;
+       unsigned int nofs_flag;
        int ret = 0;
        int ret2;
 
+       /* We hold a transaction handle open, must do a NOFS allocation. */
+       nofs_flag = memalloc_nofs_save();
        tmp = ulist_alloc(GFP_KERNEL);
+       memalloc_nofs_restore(nofs_flag);
        if (!tmp)
                return -ENOMEM;