[patch 4/5] btrfs: add nofail variant of set_extent_dirty

[David Rientjes]

Add set_extent_dirty_nofail().  This function is equivalent to
set_extent_dirty(), except that it will never fail because of allocation
failure and instead loop forever trying to allocate memory.

If the first allocation attempt fails, a warning will be emitted,
including a call trace.  Subsequent failures will suppress this warning.

This was added as a helper function for documentation and auditability.
No future callers should be added.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 fs/btrfs/extent-tree.c |    8 ++++----
 fs/btrfs/extent_io.c   |   19 +++++++++++++++++++
 fs/btrfs/extent_io.h   |    2 ++
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3831,9 +3831,9 @@ static int update_block_group(struct btrfs_trans_handle *trans,
 			spin_unlock(&cache->lock);
 			spin_unlock(&cache->space_info->lock);
 
-			set_extent_dirty(info->pinned_extents,
+			set_extent_dirty_nofail(info->pinned_extents,
 					 bytenr, bytenr + num_bytes - 1,
-					 GFP_NOFS | __GFP_NOFAIL);
+					 GFP_NOFS);
 		}
 		btrfs_put_block_group(cache);
 		total -= num_bytes;
@@ -3872,8 +3872,8 @@ static int pin_down_extent(struct btrfs_root *root,
 	spin_unlock(&cache->lock);
 	spin_unlock(&cache->space_info->lock);
 
-	set_extent_dirty(root->fs_info->pinned_extents, bytenr,
-			 bytenr + num_bytes - 1, GFP_NOFS | __GFP_NOFAIL);
+	set_extent_dirty_nofail(root->fs_info->pinned_extents, bytenr,
+			 bytenr + num_bytes - 1, GFP_NOFS);
 	return 0;
 }
 
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -940,6 +940,25 @@ int set_extent_dirty(struct extent_io_tree *tree, u64 start, u64 end,
 			      NULL, mask);
 }
 
+/*
+ * NOTE: no new callers of this function should be implemented!
+ * All memory allocations should be failable whenever possible.
+ */
+int set_extent_dirty_nofail(struct extent_io_tree *tree, u64 start, u64 end,
+		     gfp_t mask)
+{
+	int ret;
+
+	for (;;) {
+		ret = set_extent_dirty(tree, start, end, mask);
+		if (ret != -ENOMEM)
+			return ret;
+		WARN_ONCE(1, "Out of memory, no fallback implemented "
+				"(flags=0x%x)\n",
+				mask);
+	}
+}
+
 int set_extent_bits(struct extent_io_tree *tree, u64 start, u64 end,
 		    int bits, gfp_t mask)
 {
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -197,6 +197,8 @@ int set_extent_new(struct extent_io_tree *tree, u64 start, u64 end,
 		   gfp_t mask);
 int set_extent_dirty(struct extent_io_tree *tree, u64 start, u64 end,
 		     gfp_t mask);
+int set_extent_dirty_nofail(struct extent_io_tree *tree, u64 start, u64 end,
+		     gfp_t mask);
 int clear_extent_dirty(struct extent_io_tree *tree, u64 start, u64 end,
 		       gfp_t mask);
 int clear_extent_ordered(struct extent_io_tree *tree, u64 start, u64 end,
--
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