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Subject[PATCH 5.0 091/238] Btrfs: setup a nofs context for memory allocation at btrfs_create_tree()
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Filipe Manana <fdmanana@suse.com>

commit b89f6d1fcb30a8cbdc18ce00c7d93792076af453 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- 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(str
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);


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