Add btrfs_end_transaction_throttle to force writers to wait for pending commits

The existing throttle mechanism was often not sufficient to prevent
new writers from coming in and making a given transaction run forever.
This adds an explicit wait at the end of most operations so they will
allow the current transaction to close.

There is no wait inside file_write, inode updates, or cow filling, all which
have different deadlock possibilities.

This is a temporary measure until better asynchronous commit support is
added.  This code leads to stalls as it waits for data=ordered
writeback, and it really needs to be fixed.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

7 files changed, 55 insertions, 59 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3cc480b83819..52569b57692d 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1672,24 +1672,6 @@ void btrfs_mark_buffer_dirty(struct extent_buffer *buf)
         set_extent_buffer_dirty(&BTRFS_I(btree_inode)->io_tree, buf);
 }
 
-void btrfs_throttle(struct btrfs_root *root)
-{
-#if 0
-        struct backing_dev_info *bdi;
-
-        bdi = &root->fs_info->bdi;
-        if (atomic_read(&root->fs_info->throttles) &&
-            bdi_write_congested(bdi)) {
-#if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,18)
-                congestion_wait(WRITE, HZ/20);
-#else
-                blk_congestion_wait(WRITE, HZ/20);
-#endif
-
-        }
-#endif
-}
-
 void btrfs_btree_balance_dirty(struct btrfs_root *root, unsigned long nr)
 {
         /*
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index 2bc64fefe6ea..deff6b4815a7 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -70,7 +70,6 @@ int btrfs_clear_buffer_defrag_done(struct extent_buffer *buf);
 int btrfs_read_buffer(struct extent_buffer *buf, u64 parent_transid);
 u32 btrfs_csum_data(struct btrfs_root *root, char *data, u32 seed, size_t len);
 void btrfs_csum_final(u32 crc, char *result);
-void btrfs_throttle(struct btrfs_root *root);
 int btrfs_open_device(struct btrfs_device *dev);
 int btrfs_verify_block_csum(struct btrfs_root *root,
                             struct extent_buffer *buf);
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index b7f8f92daf8a..ece221cba90c 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -934,7 +934,6 @@ static ssize_t btrfs_file_write(struct file *file, const char __user *buf,
                 balance_dirty_pages_ratelimited_nr(inode->i_mapping, num_pages);
                 if (num_pages < (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
                         btrfs_btree_balance_dirty(root, 1);
-                btrfs_throttle(root);
                 cond_resched();
         }
 out:
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index cf27b5984627..bbba3350d023 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -855,10 +855,9 @@ static int btrfs_unlink(struct inode *dir, struct dentry *dentry)
                 btrfs_del_ordered_inode(inode, 1);
         }
 
-        btrfs_end_transaction(trans, root);
+        btrfs_end_transaction_throttle(trans, root);
 fail:
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return ret;
 }
 
@@ -889,10 +888,9 @@ static int btrfs_rmdir(struct inode *dir, struct dentry *dentry)
         }
 
         nr = trans->blocks_used;
-        ret = btrfs_end_transaction(trans, root);
+        ret = btrfs_end_transaction_throttle(trans, root);
 fail:
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
 
         if (ret && !err)
                 err = ret;
@@ -1871,14 +1869,13 @@ static int btrfs_mknod(struct inode *dir, struct dentry *dentry,
         btrfs_update_inode_block_group(trans, dir);
 out_unlock:
         nr = trans->blocks_used;
-        btrfs_end_transaction(trans, root);
+        btrfs_end_transaction_throttle(trans, root);
 fail:
         if (drop_inode) {
                 inode_dec_link_count(inode);
                 iput(inode);
         }
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return err;
 }
 
@@ -1936,14 +1933,13 @@ static int btrfs_create(struct inode *dir, struct dentry *dentry,
         btrfs_update_inode_block_group(trans, dir);
 out_unlock:
         nr = trans->blocks_used;
-        btrfs_end_transaction(trans, root);
+        btrfs_end_transaction_throttle(trans, root);
 fail:
         if (drop_inode) {
                 inode_dec_link_count(inode);
                 iput(inode);
         }
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return err;
 }
 
@@ -1985,14 +1981,13 @@ static int btrfs_link(struct dentry *old_dentry, struct inode *dir,
                 drop_inode = 1;
 
         nr = trans->blocks_used;
-        btrfs_end_transaction(trans, root);
+        btrfs_end_transaction_throttle(trans, root);
 fail:
         if (drop_inode) {
                 inode_dec_link_count(inode);
                 iput(inode);
         }
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return err;
 }
 
@@ -2055,13 +2050,12 @@ static int btrfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
 
 out_fail:
         nr = trans->blocks_used;
-        btrfs_end_transaction(trans, root);
+        btrfs_end_transaction_throttle(trans, root);
 
 out_unlock:
         if (drop_on_err)
                 iput(inode);
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return err;
 }
 
@@ -2587,10 +2581,9 @@ static void btrfs_truncate(struct inode *inode)
         btrfs_update_inode(trans, root, inode);
         nr = trans->blocks_used;
 
-        ret = btrfs_end_transaction(trans, root);
+        ret = btrfs_end_transaction_throttle(trans, root);
         BUG_ON(ret);
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
 }
 
 /*
@@ -2912,14 +2905,13 @@ static int btrfs_symlink(struct inode *dir, struct dentry *dentry,
 
 out_unlock:
         nr = trans->blocks_used;
-        btrfs_end_transaction(trans, root);
+        btrfs_end_transaction_throttle(trans, root);
 out_fail:
         if (drop_inode) {
                 inode_dec_link_count(inode);
                 iput(inode);
         }
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return err;
 }
 
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 6002eb64daf9..026039a2ac58 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -164,7 +164,6 @@ fail:
                 ret = err;
 fail_commit:
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return ret;
 }
 
@@ -206,7 +205,6 @@ static int create_snapshot(struct btrfs_root *root, char *name, int namelen)
 
 fail_unlock:
         btrfs_btree_balance_dirty(root, nr);
-        btrfs_throttle(root);
         return ret;
 }
 
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 5a1ee0665ae8..69ed5f85a387 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -130,8 +130,27 @@ struct btrfs_trans_handle *btrfs_start_transaction(struct btrfs_root *root,
         return h;
 }
 
-int btrfs_end_transaction(struct btrfs_trans_handle *trans,
-                          struct btrfs_root *root)
+static noinline int wait_for_commit(struct btrfs_root *root,
+                                    struct btrfs_transaction *commit)
+{
+        DEFINE_WAIT(wait);
+        mutex_lock(&root->fs_info->trans_mutex);
+        while(!commit->commit_done) {
+                prepare_to_wait(&commit->commit_wait, &wait,
+                                TASK_UNINTERRUPTIBLE);
+                if (commit->commit_done)
+                        break;
+                mutex_unlock(&root->fs_info->trans_mutex);
+                schedule();
+                mutex_lock(&root->fs_info->trans_mutex);
+        }
+        mutex_unlock(&root->fs_info->trans_mutex);
+        finish_wait(&commit->commit_wait, &wait);
+        return 0;
+}
+
+static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
+                          struct btrfs_root *root, int throttle)
 {
         struct btrfs_transaction *cur_trans;
 
@@ -140,8 +159,18 @@ int btrfs_end_transaction(struct btrfs_trans_handle *trans,
         WARN_ON(cur_trans != trans->transaction);
         WARN_ON(cur_trans->num_writers < 1);
         cur_trans->num_writers--;
+
         if (waitqueue_active(&cur_trans->writer_wait))
                 wake_up(&cur_trans->writer_wait);
+
+        if (cur_trans->in_commit && throttle) {
+                int ret;
+                mutex_unlock(&root->fs_info->trans_mutex);
+                ret = wait_for_commit(root, cur_trans);
+                BUG_ON(ret);
+                mutex_lock(&root->fs_info->trans_mutex);
+        }
+
         put_transaction(cur_trans);
         mutex_unlock(&root->fs_info->trans_mutex);
         memset(trans, 0, sizeof(*trans));
@@ -149,6 +178,18 @@ int btrfs_end_transaction(struct btrfs_trans_handle *trans,
         return 0;
 }
 
+int btrfs_end_transaction(struct btrfs_trans_handle *trans,
+                          struct btrfs_root *root)
+{
+        return __btrfs_end_transaction(trans, root, 0);
+}
+
+int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root)
+{
+        return __btrfs_end_transaction(trans, root, 1);
+}
+
 
 int btrfs_write_and_wait_transaction(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root)
@@ -240,25 +281,6 @@ int btrfs_commit_tree_roots(struct btrfs_trans_handle *trans,
         return 0;
 }
 
-static noinline int wait_for_commit(struct btrfs_root *root,
-                                    struct btrfs_transaction *commit)
-{
-        DEFINE_WAIT(wait);
-        mutex_lock(&root->fs_info->trans_mutex);
-        while(!commit->commit_done) {
-                prepare_to_wait(&commit->commit_wait, &wait,
-                                TASK_UNINTERRUPTIBLE);
-                if (commit->commit_done)
-                        break;
-                mutex_unlock(&root->fs_info->trans_mutex);
-                schedule();
-                mutex_lock(&root->fs_info->trans_mutex);
-        }
-        mutex_unlock(&root->fs_info->trans_mutex);
-        finish_wait(&commit->commit_wait, &wait);
-        return 0;
-}
-
 struct dirty_root {
         struct list_head list;
         struct btrfs_root *root;
@@ -680,6 +702,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
                              root->fs_info->btree_inode->i_mapping, GFP_NOFS);
 
         trans->transaction->in_commit = 1;
+printk("trans %Lu in commit\n", trans->transid);
         cur_trans = trans->transaction;
         if (cur_trans->list.prev != &root->fs_info->trans_list) {
                 prev_trans = list_entry(cur_trans->list.prev,
@@ -760,6 +783,7 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
         kfree(pinned_copy);
 
         cur_trans->commit_done = 1;
+printk("trans %Lu done in commit\n", cur_trans->transid);
         root->fs_info->last_trans_committed = cur_trans->transid;
         wake_up(&cur_trans->commit_wait);
         put_transaction(cur_trans);
diff --git a/fs/btrfs/transaction.h b/fs/btrfs/transaction.h
index c3172ddb3321..52559b51b181 100644
--- a/fs/btrfs/transaction.h
+++ b/fs/btrfs/transaction.h
@@ -101,4 +101,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
                              struct btrfs_root *root);
 int btrfs_write_ordered_inodes(struct btrfs_trans_handle *trans,
                                 struct btrfs_root *root);
+int btrfs_end_transaction_throttle(struct btrfs_trans_handle *trans,
+                                   struct btrfs_root *root);
 #endif