[PATCH 10/42] btrfs: protect space cache inode alloc with nofs

[Josef Bacik]

If we're allocating a new space cache inode it's likely going to be
under a transaction handle, so we need to use memalloc_nofs_save() in
order to avoid deadlocks, and more importantly lockdep messages that
make xfstests fail.

Reviewed-by: Omar Sandoval <osan...@fb.com>
Signed-off-by: Josef Bacik <jo...@toxicpanda.com>
Reviewed-by: David Sterba <dste...@suse.com>
---
 fs/btrfs/free-space-cache.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index c3888c113d81..e077ad3b4549 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -10,6 +10,7 @@
 #include <linux/math64.h>
 #include <linux/ratelimit.h>
 #include <linux/error-injection.h>
+#include <linux/sched/mm.h>
 #include "ctree.h"
 #include "free-space-cache.h"
 #include "transaction.h"
@@ -47,6 +48,7 @@ static struct inode *__lookup_free_space_inode(struct 
btrfs_root *root,
        struct btrfs_free_space_header *header;
        struct extent_buffer *leaf;
        struct inode *inode = NULL;
+       unsigned nofs_flag;
        int ret;
 
        key.objectid = BTRFS_FREE_SPACE_OBJECTID;
@@ -68,7 +70,13 @@ static struct inode *__lookup_free_space_inode(struct 
btrfs_root *root,
        btrfs_disk_key_to_cpu(&location, &disk_key);
        btrfs_release_path(path);
 
+       /*
+        * We are often under a trans handle at this point, so we need to make
+        * sure NOFS is set to keep us from deadlocking.
+        */
+       nofs_flag = memalloc_nofs_save();
        inode = btrfs_iget(fs_info->sb, &location, root, NULL);
+       memalloc_nofs_restore(nofs_flag);
        if (IS_ERR(inode))
                return inode;
 
-- 
2.14.3