FAILED: patch "[PATCH] Btrfs: fix use-after-free during inode eviction" failed to apply to 4.9-stable tree

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: Filipe Manana <[email protected]>
Date: Fri, 12 Oct 2018 13:02:48 +0100
Subject: [PATCH] Btrfs: fix use-after-free during inode eviction

At inode.c:evict_inode_truncate_pages(), when we iterate over the inode's extent states, we access an extent state record's "state" field after we unlocked the inode's io tree lock. This can lead to a use-after-free issue because after we unlock the io tree that extent state record might have been freed due to being merged into another adjacent extent state record (a previous inflight bio for a read operation finished in the meanwhile which unlocked a range in the io tree and cause a merge of extent state records, as explained in the comment before the while loop added in commit 6ca0709756710 ("Btrfs: fix hang during inode eviction due to concurrent readahead")).

Fix this by keeping a copy of the extent state's flags in a local variable and using it after unlocking the io tree.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201189

index 28625f344952..f4d31fd62eed 100644
@@ -5268,11 +5268,13 @@ static void evict_inode_truncate_pages(struct inode *inode)
 		struct extent_state *cached_state = NULL;
 		u64 start;
 		u64 end;
+		unsigned state_flags;
 
 		node = rb_first(&io_tree->state);
 		state = rb_entry(node, struct extent_state, rb_node);
 		start = state->start;
 		end = state->end;
+		state_flags = state->state;
 		spin_unlock(&io_tree->lock);
 
 		lock_extent_bits(io_tree, start, end, &cached_state);

@@ -5285,7 +5287,7 @@ static void evict_inode_truncate_pages(struct inode *inode)
 		 *
 		 * Note, end is the bytenr of last byte, so we need + 1 here.
 		 */
-		if (state->state & EXTENT_DELALLOC)
+		if (state_flags & EXTENT_DELALLOC)
 			btrfs_qgroup_free_data(inode, NULL, start, end - start + 1);
 
 		clear_extent_bit(io_tree, start, end,