btrfs: track exclusive filesystem operation in flags

There are several operations, usually started from ioctls, that cannot
run concurrently. The status is tracked in
mutually_exclusive_operation_running as an atomic_t. We can easily track
the status as one of the per-filesystem flag bits with same
synchronization guarantees.

The conversion replaces:

* atomic_xchg(..., 1)    ->   test_and_set_bit(FLAG, ...)
* atomic_set(..., 0)     ->   clear_bit(FLAG, ...)

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

4 files changed, 25 insertions, 26 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e9d77115e695..70631d773669 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -705,6 +705,11 @@ struct btrfs_delayed_root;
 #define BTRFS_FS_BTREE_ERR                      11
 #define BTRFS_FS_LOG1_ERR                       12
 #define BTRFS_FS_LOG2_ERR                       13
+/*
+ * Indicate that a whole-filesystem exclusive operation is running
+ * (device replace, resize, device add/delete, balance)
+ */
+#define BTRFS_FS_EXCL_OP                        14
 
 struct btrfs_fs_info {
         u8 fsid[BTRFS_FSID_SIZE];
@@ -1070,8 +1075,6 @@ struct btrfs_fs_info {
         /* device replace state */
         struct btrfs_dev_replace dev_replace;
 
-        atomic_t mutually_exclusive_operation_running;
-
         struct percpu_counter bio_counter;
         wait_queue_head_t replace_wait;
 
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index e653921f05d9..de7b2c897fe0 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -784,8 +784,7 @@ int btrfs_resume_dev_replace_async(struct btrfs_fs_info *fs_info)
         }
         btrfs_dev_replace_unlock(dev_replace, 1);
 
-        WARN_ON(atomic_xchg(
-                &fs_info->mutually_exclusive_operation_running, 1));
+        WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
         task = kthread_run(btrfs_dev_replace_kthread, fs_info, "btrfs-devrepl");
         return PTR_ERR_OR_ZERO(task);
 }
@@ -814,7 +813,7 @@ static int btrfs_dev_replace_kthread(void *data)
                         (unsigned int)progress);
         }
         btrfs_dev_replace_continue_on_mount(fs_info);
-        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 
         return 0;
 }
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index dabfc7ac48a6..a29dc3fd7152 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1504,7 +1504,7 @@ static noinline int btrfs_ioctl_resize(struct file *file,
         if (ret)
                 return ret;
 
-        if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+        if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
                 mnt_drop_write_file(file);
                 return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
         }
@@ -1619,7 +1619,7 @@ out_free:
         kfree(vol_args);
 out:
         mutex_unlock(&fs_info->volume_mutex);
-        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
         mnt_drop_write_file(file);
         return ret;
 }
@@ -2661,7 +2661,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
-        if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1))
+        if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags))
                 return BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
 
         mutex_lock(&fs_info->volume_mutex);
@@ -2680,7 +2680,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_fs_info *fs_info, void __user *arg)
         kfree(vol_args);
 out:
         mutex_unlock(&fs_info->volume_mutex);
-        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
         return ret;
 }
 
@@ -2708,7 +2708,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
         if (vol_args->flags & ~BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED)
                 return -EOPNOTSUPP;
 
-        if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+        if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
                 ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
                 goto out;
         }
@@ -2721,7 +2721,7 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg)
                 ret = btrfs_rm_device(fs_info, vol_args->name, 0);
         }
         mutex_unlock(&fs_info->volume_mutex);
-        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 
         if (!ret) {
                 if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID)
@@ -2752,7 +2752,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
         if (ret)
                 return ret;
 
-        if (atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+        if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
                 ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
                 goto out_drop_write;
         }
@@ -2772,7 +2772,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
                 btrfs_info(fs_info, "disk deleted %s", vol_args->name);
         kfree(vol_args);
 out:
-        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 out_drop_write:
         mnt_drop_write_file(file);
 
@@ -4442,13 +4442,11 @@ static long btrfs_ioctl_dev_replace(struct btrfs_fs_info *fs_info,
                         ret = -EROFS;
                         goto out;
                 }
-                if (atomic_xchg(
-                        &fs_info->mutually_exclusive_operation_running, 1)) {
+                if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
                         ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
                 } else {
                         ret = btrfs_dev_replace_by_ioctl(fs_info, p);
-                        atomic_set(
-                         &fs_info->mutually_exclusive_operation_running, 0);
+                        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
                 }
                 break;
         case BTRFS_IOCTL_DEV_REPLACE_CMD_STATUS:
@@ -4643,7 +4641,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
                 return ret;
 
 again:
-        if (!atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1)) {
+        if (!test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
                 mutex_lock(&fs_info->volume_mutex);
                 mutex_lock(&fs_info->balance_mutex);
                 need_unlock = true;
@@ -4689,7 +4687,7 @@ again:
         }
 
 locked:
-        BUG_ON(!atomic_read(&fs_info->mutually_exclusive_operation_running));
+        BUG_ON(!test_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
 
         if (arg) {
                 bargs = memdup_user(arg, sizeof(*bargs));
@@ -4745,11 +4743,10 @@ locked:
 
 do_balance:
         /*
-         * Ownership of bctl and mutually_exclusive_operation_running
+         * Ownership of bctl and filesystem flag BTRFS_FS_EXCL_OP
          * goes to to btrfs_balance.  bctl is freed in __cancel_balance,
          * or, if restriper was paused all the way until unmount, in
-         * free_fs_info.  mutually_exclusive_operation_running is
-         * cleared in __cancel_balance.
+         * free_fs_info.  The flag is cleared in __cancel_balance.
          */
         need_unlock = false;
 
@@ -4769,7 +4766,7 @@ out_unlock:
         mutex_unlock(&fs_info->balance_mutex);
         mutex_unlock(&fs_info->volume_mutex);
         if (need_unlock)
-                atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+                clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 out:
         mnt_drop_write_file(file);
         return ret;
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index df50a63bbc3f..2e425a909125 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3761,7 +3761,7 @@ static void __cancel_balance(struct btrfs_fs_info *fs_info)
         if (ret)
                 btrfs_handle_fs_error(fs_info, ret, NULL);
 
-        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+        clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
 }
 
 /* Non-zero return value signifies invalidity */
@@ -3941,7 +3941,7 @@ out:
                 __cancel_balance(fs_info);
         else {
                 kfree(bctl);
-                atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
+                clear_bit(BTRFS_FS_EXCL_OP, &fs_info->flags);
         }
         return ret;
 }
@@ -4031,7 +4031,7 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
         btrfs_balance_sys(leaf, item, &disk_bargs);
         btrfs_disk_balance_args_to_cpu(&bctl->sys, &disk_bargs);
 
-        WARN_ON(atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1));
+        WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
 
         mutex_lock(&fs_info->volume_mutex);
         mutex_lock(&fs_info->balance_mutex);