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 84de76a2fb217dc1b6bc2965cc397d1648aa1404 Mon Sep 17 00:00:00 2001
From: Josef Bacik josef@toxicpanda.com Date: Fri, 28 Sep 2018 07:17:49 -0400 Subject: [PATCH] btrfs: protect space cache inode alloc with GFP_NOFS
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.
CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Omar Sandoval osandov@fb.com Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c index ed097ff023e8..a1f379e8ad13 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;