Btrfs: use a worker thread to do caching

A user reported a deadlock when copying a bunch of files.  This is because they
were low on memory and kthreadd got hung up trying to migrate pages for an
allocation when starting the caching kthread.  The page was locked by the person
starting the caching kthread.  To fix this we just need to use the async thread
stuff so that the threads are already created and we don't have to worry about
deadlocks.  Thanks,

Reported-by: Roman Mamedov <rm@romanrm.ru>
Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1ac8db5dc0a3..234a08404fc2 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1807,6 +1807,9 @@ struct btrfs_root *open_ctree(struct super_block *sb,
                            fs_info->thread_pool_size),
                            &fs_info->generic_worker);
 
+        btrfs_init_workers(&fs_info->caching_workers, "cache",
+                           2, &fs_info->generic_worker);
+
         /* a higher idle thresh on the submit workers makes it much more
          * likely that bios will be send down in a sane order to the
          * devices
@@ -1860,6 +1863,7 @@ struct btrfs_root *open_ctree(struct super_block *sb,
         btrfs_start_workers(&fs_info->endio_write_workers, 1);
         btrfs_start_workers(&fs_info->endio_freespace_worker, 1);
         btrfs_start_workers(&fs_info->delayed_workers, 1);
+        btrfs_start_workers(&fs_info->caching_workers, 1);
 
         fs_info->bdi.ra_pages *= btrfs_super_num_devices(disk_super);
         fs_info->bdi.ra_pages = max(fs_info->bdi.ra_pages,
@@ -2117,6 +2121,7 @@ fail_sb_buffer:
         btrfs_stop_workers(&fs_info->endio_freespace_worker);
         btrfs_stop_workers(&fs_info->submit_workers);
         btrfs_stop_workers(&fs_info->delayed_workers);
+        btrfs_stop_workers(&fs_info->caching_workers);
 fail_alloc:
         kfree(fs_info->delayed_root);
 fail_iput:
@@ -2584,6 +2589,7 @@ int close_ctree(struct btrfs_root *root)
         btrfs_stop_workers(&fs_info->endio_freespace_worker);
         btrfs_stop_workers(&fs_info->submit_workers);
         btrfs_stop_workers(&fs_info->delayed_workers);
+        btrfs_stop_workers(&fs_info->caching_workers);
 
         btrfs_close_devices(fs_info->fs_devices);
         btrfs_mapping_tree_free(&fs_info->mapping_tree);