Btrfs: fix panic when trying to destroy a newly allocated

There is a problem where iget5_locked will look for an inode, not find it, and
then subsequently try to allocate it.  Another CPU will have raced in and
allocated the inode instead, so when iget5_locked gets the inode spin lock again
and does a search, it finds the new inode.  So it goes ahead and calls
destroy_inode on the inode it just allocated.  The problem is we don't set
BTRFS_I(inode)->root until the new inode is completely initialized.  This patch
makes us set root to NULL when alloc'ing a new inode, so when we get to
btrfs_destroy_inode and we see that root is NULL we can just free up the memory
and continue on.  This fixes the panic

http://www.kerneloops.org/submitresult.php?number=812690

Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index d3d7d46a6af2..ee92801fc5db 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5180,6 +5180,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
         ei->logged_trans = 0;
         ei->outstanding_extents = 0;
         ei->reserved_extents = 0;
+        ei->root = NULL;
         spin_lock_init(&ei->accounting_lock);
         btrfs_ordered_inode_tree_init(&ei->ordered_tree);
         INIT_LIST_HEAD(&ei->i_orphan);
@@ -5196,6 +5197,14 @@ void btrfs_destroy_inode(struct inode *inode)
         WARN_ON(inode->i_data.nrpages);
 
         /*
+         * This can happen where we create an inode, but somebody else also
+         * created the same inode and we need to destroy the one we already
+         * created.
+         */
+        if (!root)
+                goto free;
+
+        /*
          * Make sure we're properly removed from the ordered operation
          * lists.
          */
@@ -5230,6 +5239,7 @@ void btrfs_destroy_inode(struct inode *inode)
         }
         inode_tree_del(inode);
         btrfs_drop_extent_cache(inode, 0, (u64)-1, 0);
+free:
         kmem_cache_free(btrfs_inode_cachep, BTRFS_I(inode));
 }