[PATCH 6/9] btrfs: Fix NO_SPACE bug caused by delayed-iput

From: Zhaolei <zhaolei@cn.fujitsu.com>
To: <linux-btrfs@vger.kernel.org>
Cc: Zhao Lei <zhaolei@cn.fujitsu.com>
Subject: [PATCH 6/9] btrfs: Fix NO_SPACE bug caused by delayed-iput
Date: Fri, 3 Apr 2015 20:12:01 +0800	[thread overview]
Message-ID: <0285fb7e3d3ec80b5dd6c977a1f1f32551d73005.1428062473.git.zhaolei@cn.fujitsu.com> (raw)
In-Reply-To: <cover.1428062473.git.zhaolei@cn.fujitsu.com>

From: Zhao Lei <zhaolei@cn.fujitsu.com>

Steps to reproduce:
  while true; do
    dd if=/dev/zero of=/btrfs_dir/file count=[fs_size * 75%]
    rm /btrfs_dir/file
    sync
  done

  And we'll see dd failed because btrfs return NO_SPACE.

Reason:
  Normally, btrfs_commit_transaction() call btrfs_run_delayed_iputs()
  in end to free fs space for next write, but sometimes it hadn't
  done work on time, because btrfs-cleaner thread get delayed-iputs
  from list before, but do iput() after next write.

  This is log:
  [ 2569.050776] comm=btrfs-cleaner func=btrfs_evict_inode() begin

  [ 2569.084280] comm=sync func=btrfs_commit_transaction() call btrfs_run_delayed_iputs()
  [ 2569.085418] comm=sync func=btrfs_commit_transaction() done btrfs_run_delayed_iputs()
  [ 2569.087554] comm=sync func=btrfs_commit_transaction() end

  [ 2569.191081] comm=dd begin
  [ 2569.790112] comm=dd func=__btrfs_buffered_write() ret=-28

  [ 2569.847479] comm=btrfs-cleaner func=add_pinned_bytes() 0 + 32677888 = 32677888
  [ 2569.849530] comm=btrfs-cleaner func=add_pinned_bytes() 32677888 + 23834624 = 56512512
  ...
  [ 2569.903893] comm=btrfs-cleaner func=add_pinned_bytes() 943976448 + 21762048 = 965738496
  [ 2569.908270] comm=btrfs-cleaner func=btrfs_evict_inode() end

Fix:
  Make btrfs_commit_transaction() wait current running btrfs-cleaner's
  delayed-iputs() done in end.

Test:
  Use script similar to above(more complex),
  before patch:
    7 failed in 100 * 20 loop.
  after patch:
    0 failed in 100 * 20 loop.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 fs/btrfs/ctree.h       | 1 +
 fs/btrfs/disk-io.c     | 5 ++++-
 fs/btrfs/transaction.c | 6 +++++-
 3 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index f9c89ca..54d4d78 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1513,6 +1513,7 @@ struct btrfs_fs_info {
 
 	spinlock_t delayed_iput_lock;
 	struct list_head delayed_iputs;
+	struct rw_semaphore delayed_iput_sem;
 
 	/* this protects tree_mod_seq_list */
 	spinlock_t tree_mod_seq_lock;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 639f266..df40f60 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1778,7 +1778,9 @@ static int cleaner_kthread(void *arg)
 			goto sleep;
 		}
 
+		down_read(&root->fs_info->delayed_iput_sem);
 		btrfs_run_delayed_iputs(root);
+		up_read(&root->fs_info->delayed_iput_sem);
 		btrfs_delete_unused_bgs(root->fs_info);
 		again = btrfs_clean_one_deleted_snapshot(root);
 		mutex_unlock(&root->fs_info->cleaner_mutex);
@@ -2241,11 +2243,12 @@ int open_ctree(struct super_block *sb,
 	spin_lock_init(&fs_info->qgroup_op_lock);
 	spin_lock_init(&fs_info->buffer_lock);
 	spin_lock_init(&fs_info->unused_bgs_lock);
-	mutex_init(&fs_info->unused_bg_unpin_mutex);
 	rwlock_init(&fs_info->tree_mod_log_lock);
+	mutex_init(&fs_info->unused_bg_unpin_mutex);
 	mutex_init(&fs_info->reloc_mutex);
 	mutex_init(&fs_info->delalloc_root_mutex);
 	seqlock_init(&fs_info->profiles_lock);
+	init_rwsem(&fs_info->delayed_iput_sem);
 
 	init_completion(&fs_info->kobj_unregister);
 	INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 8be4278..d18991f 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -2076,8 +2076,12 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 
 	kmem_cache_free(btrfs_trans_handle_cachep, trans);
 
-	if (current != root->fs_info->transaction_kthread)
+	if (current != root->fs_info->transaction_kthread) {
 		btrfs_run_delayed_iputs(root);
+		/* make sure that all running delayed iput are done */
+		down_write(&root->fs_info->delayed_iput_sem);
+		up_write(&root->fs_info->delayed_iput_sem);
+	}
 
 	return ret;
 
-- 
1.8.5.1

