Btrfs: fix deadlock during allocating chunks

This deadlock comes from xfstests 251.

We'll hold the chunk_mutex throughout the whole of a chunk allocation.
But if we find that we've used up system chunk space, we need to allocate a
new system chunk, but this will lead to a recursion of chunk allocation and end
up with a deadlock on chunk_mutex.
So instead we need to allocate the system chunk first if we find we're in ENOSPC.

Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7c23340..a844204 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3445,6 +3445,50 @@ static int should_alloc_chunk(struct btrfs_root *root,
        return 1;
 }
 
+static u64 get_system_chunk_thresh(struct btrfs_root *root, u64 type)
+{
+       u64 num_dev;
+
+       if (type & BTRFS_BLOCK_GROUP_RAID10 ||
+           type & BTRFS_BLOCK_GROUP_RAID0)
+               num_dev = root->fs_info->fs_devices->rw_devices;
+       else if (type & BTRFS_BLOCK_GROUP_RAID1)
+               num_dev = 2;
+       else
+               num_dev = 1;    /* DUP or single */
+
+       /* metadata for updaing devices and chunk tree */
+       return btrfs_calc_trans_metadata_size(root, num_dev + 1);
+}
+
+static void check_system_chunk(struct btrfs_trans_handle *trans,
+                              struct btrfs_root *root, u64 type)
+{
+       struct btrfs_space_info *info;
+       u64 left;
+       u64 thresh;
+
+       info = __find_space_info(root->fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
+       spin_lock(&info->lock);
+       left = info->total_bytes - info->bytes_used - info->bytes_pinned -
+               info->bytes_reserved - info->bytes_readonly;
+       spin_unlock(&info->lock);
+
+       thresh = get_system_chunk_thresh(root, type);
+       if (left < thresh && btrfs_test_opt(root, ENOSPC_DEBUG)) {
+               printk(KERN_INFO "left=%llu, need=%llu, flags=%llu\n",
+                      left, thresh, type);
+               dump_space_info(info, 0, 0);
+       }
+
+       if (left < thresh) {
+               u64 flags;
+
+               flags = btrfs_get_alloc_profile(root->fs_info->chunk_root, 0);
+               btrfs_alloc_chunk(trans, root, flags);
+       }
+}
+
 static int do_chunk_alloc(struct btrfs_trans_handle *trans,
                          struct btrfs_root *extent_root, u64 alloc_bytes,
                          u64 flags, int force)
@@ -3515,6 +3559,12 @@ again:
                        force_metadata_allocation(fs_info);
        }
 
+       /*
+        * Check if we have enough space in SYSTEM chunk because we may need
+        * to update devices.
+        */
+       check_system_chunk(trans, extent_root, flags);
+
        ret = btrfs_alloc_chunk(trans, extent_root, flags);
        if (ret < 0 && ret != -ENOSPC)
                goto out;