btrfs: track running balance in a simpler way

Currently fs_info::balance_running is 0 or 1 and does not use the
semantics of atomics. The pause and cancel check for 0, that can happen
only after __btrfs_balance exits for whatever reason.

Parallel calls to balance ioctl may enter btrfs_ioctl_balance multiple
times but will block on the balance_mutex that protects the
fs_info::flags bit.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index add0e5a..8fdc973 100644 (file)
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -739,6 +739,12 @@ struct btrfs_delayed_root;
  */
 #define BTRFS_FS_NEED_ASYNC_COMMIT             17
 
+/*
+ * Indicate that balance has been set up from the ioctl and is in the main
+ * phase. The fs_info::balance_ctl is initialized.
+ */
+#define BTRFS_FS_BALANCE_RUNNING               18
+
 struct btrfs_fs_info {
        u8 fsid[BTRFS_FSID_SIZE];
        u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
@@ -1003,7 +1009,6 @@ struct btrfs_fs_info {
        /* restriper state */
        spinlock_t balance_lock;
        struct mutex balance_mutex;
-       atomic_t balance_running;
        atomic_t balance_pause_req;
        atomic_t balance_cancel_req;
        struct btrfs_balance_control *balance_ctl;

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 49a990c..7503ff1 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2164,7 +2164,6 @@ static void btrfs_init_balance(struct btrfs_fs_info *fs_info)
 {
        spin_lock_init(&fs_info->balance_lock);
        mutex_init(&fs_info->balance_mutex);
-       atomic_set(&fs_info->balance_running, 0);
        atomic_set(&fs_info->balance_pause_req, 0);
        atomic_set(&fs_info->balance_cancel_req, 0);
        fs_info->balance_ctl = NULL;

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index c690092..ffb224b 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4312,7 +4312,7 @@ void update_ioctl_balance_args(struct btrfs_fs_info *fs_info, int lock,
 
        bargs->flags = bctl->flags;
 
-       if (atomic_read(&fs_info->balance_running))
+       if (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags))
                bargs->state |= BTRFS_BALANCE_STATE_RUNNING;
        if (atomic_read(&fs_info->balance_pause_req))
                bargs->state |= BTRFS_BALANCE_STATE_PAUSE_REQ;
@@ -4364,7 +4364,7 @@ again:
        mutex_lock(&fs_info->balance_mutex);
        if (fs_info->balance_ctl) {
                /* this is either (2) or (3) */
-               if (!atomic_read(&fs_info->balance_running)) {
+               if (!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
                        mutex_unlock(&fs_info->balance_mutex);
                        /*
                         * Lock released to allow other waiters to continue,
@@ -4373,7 +4373,7 @@ again:
                        mutex_lock(&fs_info->balance_mutex);
 
                        if (fs_info->balance_ctl &&
-                           !atomic_read(&fs_info->balance_running)) {
+                           !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
                                /* this is (3) */
                                need_unlock = false;
                                goto locked;

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 0216bc8..ed23024 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3907,13 +3907,14 @@ int btrfs_balance(struct btrfs_balance_control *bctl,
                spin_unlock(&fs_info->balance_lock);
        }
 
-       atomic_inc(&fs_info->balance_running);
+       ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
+       set_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);
        mutex_unlock(&fs_info->balance_mutex);
 
        ret = __btrfs_balance(fs_info);
 
        mutex_lock(&fs_info->balance_mutex);
-       atomic_dec(&fs_info->balance_running);
+       clear_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags);
 
        if (bargs) {
                memset(bargs, 0, sizeof(*bargs));
@@ -4061,16 +4062,16 @@ int btrfs_pause_balance(struct btrfs_fs_info *fs_info)
                return -ENOTCONN;
        }
 
-       if (atomic_read(&fs_info->balance_running)) {
+       if (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
                atomic_inc(&fs_info->balance_pause_req);
                mutex_unlock(&fs_info->balance_mutex);
 
                wait_event(fs_info->balance_wait_q,
-                          atomic_read(&fs_info->balance_running) == 0);
+                          !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
 
                mutex_lock(&fs_info->balance_mutex);
                /* we are good with balance_ctl ripped off from under us */
-               BUG_ON(atomic_read(&fs_info->balance_running));
+               BUG_ON(test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
                atomic_dec(&fs_info->balance_pause_req);
        } else {
                ret = -ENOTCONN;
@@ -4096,10 +4097,10 @@ int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
         * if we are running just wait and return, balance item is
         * deleted in btrfs_balance in this case
         */
-       if (atomic_read(&fs_info->balance_running)) {
+       if (test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags)) {
                mutex_unlock(&fs_info->balance_mutex);
                wait_event(fs_info->balance_wait_q,
-                          atomic_read(&fs_info->balance_running) == 0);
+                          !test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
                mutex_lock(&fs_info->balance_mutex);
        } else {
                mutex_unlock(&fs_info->balance_mutex);
@@ -4115,7 +4116,8 @@ int btrfs_cancel_balance(struct btrfs_fs_info *fs_info)
                }
        }
 
-       BUG_ON(fs_info->balance_ctl || atomic_read(&fs_info->balance_running));
+       BUG_ON(fs_info->balance_ctl ||
+               test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
        atomic_dec(&fs_info->balance_cancel_req);
        mutex_unlock(&fs_info->balance_mutex);
        return 0;