Btrfs: fix qgroup rescan resume on mount

When called during mount, we cannot start the rescan worker thread until
open_ctree is done. This commit restuctures the qgroup rescan internals to
enable a clean deferral of the rescan resume operation.

First of all, the struct qgroup_rescan is removed, saving us a malloc and
some initialization synchronizations problems. Its only element (the worker
struct) now lives within fs_info just as the rest of the rescan code.

Then setting up a rescan worker is split into several reusable stages.
Currently we have three different rescan startup scenarios:
	(A) rescan ioctl
	(B) rescan resume by mount
	(C) rescan by quota enable

Each case needs its own combination of the four following steps:
	(1) set the progress [A, C: zero; B: state of umount]
	(2) commit the transaction [A]
	(3) set the counters [A, C: zero; B: state of umount]
	(4) start worker [A, B, C]

qgroup_rescan_init does step (1). There's no extra function added to commit
a transaction, we've got that already. qgroup_rescan_zero_tracking does
step (3). Step (4) is nothing more than a call to the generic
btrfs_queue_worker.

We also get rid of a double check for the rescan progress during
btrfs_qgroup_account_ref, which is no longer required due to having step 2
from the list above.

As a side effect, this commit prepares to move the rescan start code from
btrfs_run_qgroups (which is run during commit) to a less time critical
section.

Signed-off-by: Jan Schmidt <list.btrfs@jan-o-sch.net>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

3 files changed, 125 insertions, 69 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index a07b8c0a260d..80ab1a6f4fe3 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1609,6 +1609,7 @@ struct btrfs_fs_info {
         struct btrfs_key qgroup_rescan_progress;
         struct btrfs_workers qgroup_rescan_workers;
         struct completion qgroup_rescan_completion;
+        struct btrfs_work qgroup_rescan_work;
 
         /* filesystem state */
         unsigned long fs_state;
@@ -3858,6 +3859,7 @@ int btrfs_quota_enable(struct btrfs_trans_handle *trans,
 int btrfs_quota_disable(struct btrfs_trans_handle *trans,
                         struct btrfs_fs_info *fs_info);
 int btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info);
+void btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info);
 int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info);
 int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans,
                               struct btrfs_fs_info *fs_info, u64 src, u64 dst);
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b9eaa0f21144..9b7020197c71 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2879,6 +2879,8 @@ retry_root_backup:
                 return ret;
         }
 
+        btrfs_qgroup_rescan_resume(fs_info);
+
         return 0;
 
 fail_qgroup:
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index c6ce64276869..1280eff8af56 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -98,13 +98,10 @@ struct btrfs_qgroup_list {
         struct btrfs_qgroup *member;
 };
 
-struct qgroup_rescan {
-        struct btrfs_work       work;
-        struct btrfs_fs_info    *fs_info;
-};
-
-static void qgroup_rescan_start(struct btrfs_fs_info *fs_info,
-                                struct qgroup_rescan *qscan);
+static int
+qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
+                   int init_flags);
+static void qgroup_rescan_zero_tracking(struct btrfs_fs_info *fs_info);
 
 /* must be called with qgroup_ioctl_lock held */
 static struct btrfs_qgroup *find_qgroup_rb(struct btrfs_fs_info *fs_info,
@@ -255,6 +252,7 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
         int slot;
         int ret = 0;
         u64 flags = 0;
+        u64 rescan_progress = 0;
 
         if (!fs_info->quota_enabled)
                 return 0;
@@ -312,20 +310,7 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
                         }
                         fs_info->qgroup_flags = btrfs_qgroup_status_flags(l,
                                                                           ptr);
-                        fs_info->qgroup_rescan_progress.objectid =
-                                        btrfs_qgroup_status_rescan(l, ptr);
-                        if (fs_info->qgroup_flags &
-                            BTRFS_QGROUP_STATUS_FLAG_RESCAN) {
-                                struct qgroup_rescan *qscan =
-                                        kmalloc(sizeof(*qscan), GFP_NOFS);
-                                if (!qscan) {
-                                        ret = -ENOMEM;
-                                        goto out;
-                                }
-                                fs_info->qgroup_rescan_progress.type = 0;
-                                fs_info->qgroup_rescan_progress.offset = 0;
-                                qgroup_rescan_start(fs_info, qscan);
-                        }
+                        rescan_progress = btrfs_qgroup_status_rescan(l, ptr);
                         goto next1;
                 }
 
@@ -427,12 +412,16 @@ out:
         if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON)) {
                 fs_info->quota_enabled = 0;
                 fs_info->pending_quota_state = 0;
+        } else if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN &&
+                   ret >= 0) {
+                ret = qgroup_rescan_init(fs_info, rescan_progress, 0);
         }
         btrfs_free_path(path);
 
         if (ret < 0) {
                 ulist_free(fs_info->qgroup_ulist);
                 fs_info->qgroup_ulist = NULL;
+                fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
         }
 
         return ret < 0 ? ret : 0;
@@ -1449,14 +1438,7 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
         if (ret < 0)
                 return ret;
 
-        mutex_lock(&fs_info->qgroup_rescan_lock);
         spin_lock(&fs_info->qgroup_lock);
-        if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) {
-                if (fs_info->qgroup_rescan_progress.objectid <= node->bytenr) {
-                        ret = 0;
-                        goto unlock;
-                }
-        }
 
         quota_root = fs_info->quota_root;
         if (!quota_root)
@@ -1496,7 +1478,6 @@ int btrfs_qgroup_account_ref(struct btrfs_trans_handle *trans,
 
 unlock:
         spin_unlock(&fs_info->qgroup_lock);
-        mutex_unlock(&fs_info->qgroup_rescan_lock);
         ulist_free(roots);
 
         return ret;
@@ -1544,9 +1525,12 @@ int btrfs_run_qgroups(struct btrfs_trans_handle *trans,
                 fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
 
         if (!ret && start_rescan_worker) {
-                ret = btrfs_qgroup_rescan(fs_info);
-                if (ret)
-                        pr_err("btrfs: start rescan quota failed: %d\n", ret);
+                ret = qgroup_rescan_init(fs_info, 0, 1);
+                if (!ret) {
+                        qgroup_rescan_zero_tracking(fs_info);
+                        btrfs_queue_worker(&fs_info->qgroup_rescan_workers,
+                                           &fs_info->qgroup_rescan_work);
+                }
                 ret = 0;
         }
 
@@ -1880,12 +1864,11 @@ void assert_qgroups_uptodate(struct btrfs_trans_handle *trans)
  * returns 1 when done, 2 when done and FLAG_INCONSISTENT was cleared.
  */
 static int
-qgroup_rescan_leaf(struct qgroup_rescan *qscan, struct btrfs_path *path,
+qgroup_rescan_leaf(struct btrfs_fs_info *fs_info, struct btrfs_path *path,
                    struct btrfs_trans_handle *trans, struct ulist *tmp,
                    struct extent_buffer *scratch_leaf)
 {
         struct btrfs_key found;
-        struct btrfs_fs_info *fs_info = qscan->fs_info;
         struct ulist *roots = NULL;
         struct ulist_node *unode;
         struct ulist_iterator uiter;
@@ -2013,11 +1996,10 @@ out:
 
 static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
 {
-        struct qgroup_rescan *qscan = container_of(work, struct qgroup_rescan,
-                                                   work);
+        struct btrfs_fs_info *fs_info = container_of(work, struct btrfs_fs_info,
+                                                     qgroup_rescan_work);
         struct btrfs_path *path;
         struct btrfs_trans_handle *trans = NULL;
-        struct btrfs_fs_info *fs_info = qscan->fs_info;
         struct ulist *tmp = NULL;
         struct extent_buffer *scratch_leaf = NULL;
         int err = -ENOMEM;
@@ -2042,7 +2024,7 @@ static void btrfs_qgroup_rescan_worker(struct btrfs_work *work)
                 if (!fs_info->quota_enabled) {
                         err = -EINTR;
                 } else {
-                        err = qgroup_rescan_leaf(qscan, path, trans,
+                        err = qgroup_rescan_leaf(fs_info, path, trans,
                                                  tmp, scratch_leaf);
                 }
                 if (err > 0)
@@ -2055,7 +2037,6 @@ out:
         kfree(scratch_leaf);
         ulist_free(tmp);
         btrfs_free_path(path);
-        kfree(qscan);
 
         mutex_lock(&fs_info->qgroup_rescan_lock);
         fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
@@ -2078,46 +2059,70 @@ out:
         complete_all(&fs_info->qgroup_rescan_completion);
 }
 
-static void
-qgroup_rescan_start(struct btrfs_fs_info *fs_info, struct qgroup_rescan *qscan)
-{
-        memset(&qscan->work, 0, sizeof(qscan->work));
-        qscan->work.func = btrfs_qgroup_rescan_worker;
-        qscan->fs_info = fs_info;
-
-        pr_info("btrfs: qgroup scan started\n");
-        btrfs_queue_worker(&fs_info->qgroup_rescan_workers, &qscan->work);
-}
-
-int
-btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
+/*
+ * Checks that (a) no rescan is running and (b) quota is enabled. Allocates all
+ * memory required for the rescan context.
+ */
+static int
+qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
+                   int init_flags)
 {
         int ret = 0;
-        struct rb_node *n;
-        struct btrfs_qgroup *qgroup;
-        struct qgroup_rescan *qscan = kmalloc(sizeof(*qscan), GFP_NOFS);
 
-        if (!qscan)
-                return -ENOMEM;
+        if (!init_flags &&
+            (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN) ||
+             !(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))) {
+                ret = -EINVAL;
+                goto err;
+        }
 
         mutex_lock(&fs_info->qgroup_rescan_lock);
         spin_lock(&fs_info->qgroup_lock);
-        if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN)
-                ret = -EINPROGRESS;
-        else if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))
-                ret = -EINVAL;
-        if (ret) {
-                spin_unlock(&fs_info->qgroup_lock);
-                mutex_unlock(&fs_info->qgroup_rescan_lock);
-                kfree(qscan);
-                return ret;
+
+        if (init_flags) {
+                if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN)
+                        ret = -EINPROGRESS;
+                else if (!(fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_ON))
+                        ret = -EINVAL;
+
+                if (ret) {
+                        spin_unlock(&fs_info->qgroup_lock);
+                        mutex_unlock(&fs_info->qgroup_rescan_lock);
+                        goto err;
+                }
+
+                fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_RESCAN;
         }
 
-        fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_RESCAN;
         memset(&fs_info->qgroup_rescan_progress, 0,
                 sizeof(fs_info->qgroup_rescan_progress));
+        fs_info->qgroup_rescan_progress.objectid = progress_objectid;
+
+        spin_unlock(&fs_info->qgroup_lock);
+        mutex_unlock(&fs_info->qgroup_rescan_lock);
+
         init_completion(&fs_info->qgroup_rescan_completion);
 
+        memset(&fs_info->qgroup_rescan_work, 0,
+               sizeof(fs_info->qgroup_rescan_work));
+        fs_info->qgroup_rescan_work.func = btrfs_qgroup_rescan_worker;
+
+        if (ret) {
+err:
+                pr_info("btrfs: qgroup_rescan_init failed with %d\n", ret);
+                return ret;
+        }
+
+        return 0;
+}
+
+static void
+qgroup_rescan_zero_tracking(struct btrfs_fs_info *fs_info)
+{
+        struct rb_node *n;
+        struct btrfs_qgroup *qgroup;
+
+        spin_lock(&fs_info->qgroup_lock);
         /* clear all current qgroup tracking information */
         for (n = rb_first(&fs_info->qgroup_tree); n; n = rb_next(n)) {
                 qgroup = rb_entry(n, struct btrfs_qgroup, node);
@@ -2127,9 +2132,44 @@ btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
                 qgroup->excl_cmpr = 0;
         }
         spin_unlock(&fs_info->qgroup_lock);
-        mutex_unlock(&fs_info->qgroup_rescan_lock);
+}
 
-        qgroup_rescan_start(fs_info, qscan);
+int
+btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info)
+{
+        int ret = 0;
+        struct btrfs_trans_handle *trans;
+
+        ret = qgroup_rescan_init(fs_info, 0, 1);
+        if (ret)
+                return ret;
+
+        /*
+         * We have set the rescan_progress to 0, which means no more
+         * delayed refs will be accounted by btrfs_qgroup_account_ref.
+         * However, btrfs_qgroup_account_ref may be right after its call
+         * to btrfs_find_all_roots, in which case it would still do the
+         * accounting.
+         * To solve this, we're committing the transaction, which will
+         * ensure we run all delayed refs and only after that, we are
+         * going to clear all tracking information for a clean start.
+         */
+
+        trans = btrfs_join_transaction(fs_info->fs_root);
+        if (IS_ERR(trans)) {
+                fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+                return PTR_ERR(trans);
+        }
+        ret = btrfs_commit_transaction(trans, fs_info->fs_root);
+        if (ret) {
+                fs_info->qgroup_flags &= ~BTRFS_QGROUP_STATUS_FLAG_RESCAN;
+                return ret;
+        }
+
+        qgroup_rescan_zero_tracking(fs_info);
+
+        btrfs_queue_worker(&fs_info->qgroup_rescan_workers,
+                           &fs_info->qgroup_rescan_work);
 
         return 0;
 }
@@ -2151,3 +2191,15 @@ int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info)
 
         return ret;
 }
+
+/*
+ * this is only called from open_ctree where we're still single threaded, thus
+ * locking is omitted here.
+ */
+void
+btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info)
+{
+        if (fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_RESCAN)
+                btrfs_queue_worker(&fs_info->qgroup_rescan_workers,
+                                   &fs_info->qgroup_rescan_work);
+}