Btrfs: setup a nofs context for memory allocation at btrfs_create_tree()

From: Filipe Manana <[email protected]>

We are holding a transaction handle when creating a tree, therefore we can not allocate the root using GFP_KERNEL, as we could deadlock if reclaim is triggered by the allocation, therefore setup a nofs context.

Fixes 74e4d82757f74 ("btrfs: let callers of btrfs_alloc_root pass gfp flags")

Signed-off-by Filipe Manana <[email protected]>

---
 fs/btrfs/disk-io.c | 8 ++++++++
 1 file changed, 8 insertions(+)

fs/btrfs/disk-io.c +8 -0

index 67afeaf28a41..3e1b846156dd 100644
@@ -17,6 +17,7 @@
 #include <linux/semaphore.h>
 #include <linux/error-injection.h>
 #include <linux/crc32c.h>
+#include <linux/sched/mm.h>
 #include <asm/unaligned.h>
 #include "ctree.h"
 #include "disk-io.h"

@@ -1235,10 +1236,17 @@ struct btrfs_root *btrfs_create_tree(struct btrfs_trans_handle *trans,
 	struct btrfs_root *tree_root = fs_info->tree_root;
 	struct btrfs_root *root;
 	struct btrfs_key key;
+	unsigned int nofs_flag;
 	int ret = 0;
 	uuid_le uuid = NULL_UUID_LE;
 
+	/*
+	 * We're holding a transaction handle, so use a NOFS memory allocation
+	 * context to avoid deadlock if reclaim happens.
+	 */
+	nofs_flag = memalloc_nofs_save();
 	root = btrfs_alloc_root(fs_info, GFP_KERNEL);
+	memalloc_nofs_restore(nofs_flag);
 	if (!root)
 		return ERR_PTR(-ENOMEM);
 

From: Filipe Manana <[email protected]>

We are holding a transaction handle when creating a tree, therefore we can not allocate the root using GFP_KERNEL, as we could deadlock if reclaim is triggered by the allocation, therefore setup a nofs context.

Fixes 74e4d82757f74 ("btrfs: let callers of btrfs_alloc_root pass gfp flags")

Signed-off-by Filipe Manana <[email protected]>