From: Filipe Manana <fdmanana@suse.com>
Date: Thu, 13 Dec 2018 21:16:45 +0000
Git-commit: b89f6d1fcb30a8cbdc18ce00c7d93792076af453
Patch-mainline: 5.1
References: bsc#1172127
Subject: [PATCH] Btrfs: setup a nofs context for memory allocation at
 btrfs_create_tree()

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")
CC: stable@vger.kernel.org # 4.9+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/disk-io.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c7824aeec02b..047a194155fb 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -30,6 +30,7 @@
 #include <linux/ratelimit.h>
 #include <linux/uuid.h>
 #include <linux/semaphore.h>
+#include <linux/sched/mm.h>
 #include <asm/unaligned.h>
 #include "ctree.h"
 #include "disk-io.h"
@@ -1321,10 +1322,17 @@ 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;
 
+	/*
+	 * 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);
 
-- 
2.16.4