The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b89f6d1fcb30a8cbdc18ce00c7d93792076af453 Mon Sep 17 00:00:00 2001

From: Filipe Manana fdmanana@suse.com Date: Thu, 13 Dec 2018 21:16:45 +0000 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

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 6a2a2a951705..888d72dda794 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -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" @@ -1258,10 +1259,17 @@ 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);