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FAILED: patch "[PATCH] Btrfs: setup a nofs context for memory allocation at" failed to apply to 4.9-stable tree

PATCH [email protected] 1 participant 1 message Mar 20, 2019

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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 <[email protected]>.

thanks,

greg k-h

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

From b89f6d1fcb30a8cbdc18ce00c7d93792076af453 Mon Sep 17 00:00:00 2001
From: Filipe Manana <[email protected]>
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 [email protected] # 4.9+
Reviewed-by Nikolay Borisov <[email protected]>
Signed-off-by Filipe Manana <[email protected]>
Reviewed-by David Sterba <[email protected]>
Signed-off-by David Sterba <[email protected]>
fs/btrfs/disk-io.c +8 -0
index 6a2a2a951705..888d72dda794 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"

@@ -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);