linux-kernel - [PATCH 4.5 128/128] btrfs: make state preallocation more speculative in __set_extent

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Date:	Sun,  5 Jun 2016 15:24:43 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, David Sterba <dsterba@...e.com>
Subject: [PATCH 4.5 128/128] btrfs: make state preallocation more speculative in __set_extent_bit

4.5-stable review patch.  If anyone has any objections, please let me know.

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

From: David Sterba <dsterba@...e.com>

commit 059f791c6bbaba72dc3c1bd6e2657aacc8552849 upstream.

Similar to __clear_extent_bit, do not fail if the state preallocation
fails as we might not need it. One less BUG_ON.

Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/btrfs/extent_io.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -875,8 +875,14 @@ __set_extent_bit(struct extent_io_tree *
 	bits |= EXTENT_FIRST_DELALLOC;
 again:
 	if (!prealloc && gfpflags_allow_blocking(mask)) {
+		/*
+		 * Don't care for allocation failure here because we might end
+		 * up not needing the pre-allocated extent state at all, which
+		 * is the case if we only have in the tree extent states that
+		 * cover our input range and don't cover too any other range.
+		 * If we end up needing a new extent state we allocate it later.
+		 */
 		prealloc = alloc_extent_state(mask);
-		BUG_ON(!prealloc);
 	}
 
 	spin_lock(&tree->lock);