Btrfs: disallow mutually exclusive admin operations from user mode

Btrfs admin operations that are manually started from user mode
and that cannot be executed at the same time return -EINPROGRESS.
A common way to enter and leave this locked section is introduced
since it used to be specific to the balance operation.

Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

3 files changed, 40 insertions, 17 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 147406d0f9a9..e9dc78014f09 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1527,6 +1527,8 @@ struct btrfs_fs_info {
 
         /* device replace state */
         struct btrfs_dev_replace dev_replace;
+
+        atomic_t mutually_exclusive_operation_running;
 };
 
 /*
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index b40b827f93e7..26f46dad3b0e 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1317,13 +1317,13 @@ static noinline int btrfs_ioctl_resize(struct btrfs_root *root,
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
-        mutex_lock(&root->fs_info->volume_mutex);
-        if (root->fs_info->balance_ctl) {
-                printk(KERN_INFO "btrfs: balance in progress\n");
-                ret = -EINVAL;
-                goto out;
+        if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+                        1)) {
+                pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+                return -EINPROGRESS;
         }
 
+        mutex_lock(&root->fs_info->volume_mutex);
         vol_args = memdup_user(arg, sizeof(*vol_args));
         if (IS_ERR(vol_args)) {
                 ret = PTR_ERR(vol_args);
@@ -1419,6 +1419,7 @@ out_free:
         kfree(vol_args);
 out:
         mutex_unlock(&root->fs_info->volume_mutex);
+        atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
         return ret;
 }
 
@@ -2160,9 +2161,17 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
         if (btrfs_root_readonly(root))
                 return -EROFS;
 
+        if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+                        1)) {
+                pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+                return -EINPROGRESS;
+        }
         ret = mnt_want_write_file(file);
-        if (ret)
+        if (ret) {
+                atomic_set(&root->fs_info->mutually_exclusive_operation_running,
+                           0);
                 return ret;
+        }
 
         switch (inode->i_mode & S_IFMT) {
         case S_IFDIR:
@@ -2214,6 +2223,7 @@ static int btrfs_ioctl_defrag(struct file *file, void __user *argp)
         }
 out:
         mnt_drop_write_file(file);
+        atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
         return ret;
 }
 
@@ -2225,13 +2235,13 @@ static long btrfs_ioctl_add_dev(struct btrfs_root *root, void __user *arg)
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
 
-        mutex_lock(&root->fs_info->volume_mutex);
-        if (root->fs_info->balance_ctl) {
-                printk(KERN_INFO "btrfs: balance in progress\n");
-                ret = -EINVAL;
-                goto out;
+        if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+                        1)) {
+                pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+                return -EINPROGRESS;
         }
 
+        mutex_lock(&root->fs_info->volume_mutex);
         vol_args = memdup_user(arg, sizeof(*vol_args));
         if (IS_ERR(vol_args)) {
                 ret = PTR_ERR(vol_args);
@@ -2244,6 +2254,7 @@ static long btrfs_ioctl_add_dev(struct btrfs_root *root, void __user *arg)
         kfree(vol_args);
 out:
         mutex_unlock(&root->fs_info->volume_mutex);
+        atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
         return ret;
 }
 
@@ -2258,13 +2269,13 @@ static long btrfs_ioctl_rm_dev(struct btrfs_root *root, void __user *arg)
         if (root->fs_info->sb->s_flags & MS_RDONLY)
                 return -EROFS;
 
-        mutex_lock(&root->fs_info->volume_mutex);
-        if (root->fs_info->balance_ctl) {
-                printk(KERN_INFO "btrfs: balance in progress\n");
-                ret = -EINVAL;
-                goto out;
+        if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+                        1)) {
+                pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
+                return -EINPROGRESS;
         }
 
+        mutex_lock(&root->fs_info->volume_mutex);
         vol_args = memdup_user(arg, sizeof(*vol_args));
         if (IS_ERR(vol_args)) {
                 ret = PTR_ERR(vol_args);
@@ -2277,6 +2288,7 @@ static long btrfs_ioctl_rm_dev(struct btrfs_root *root, void __user *arg)
         kfree(vol_args);
 out:
         mutex_unlock(&root->fs_info->volume_mutex);
+        atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
         return ret;
 }
 
@@ -3319,6 +3331,7 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
         struct btrfs_ioctl_balance_args *bargs;
         struct btrfs_balance_control *bctl;
         int ret;
+        int need_to_clear_lock = 0;
 
         if (!capable(CAP_SYS_ADMIN))
                 return -EPERM;
@@ -3354,10 +3367,13 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
                 bargs = NULL;
         }
 
-        if (fs_info->balance_ctl) {
+        if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
+                        1)) {
+                pr_info("btrfs: dev add/delete/balance/replace/resize operation in progress\n");
                 ret = -EINPROGRESS;
                 goto out_bargs;
         }
+        need_to_clear_lock = 1;
 
         bctl = kzalloc(sizeof(*bctl), GFP_NOFS);
         if (!bctl) {
@@ -3391,6 +3407,9 @@ do_balance:
 out_bargs:
         kfree(bargs);
 out:
+        if (need_to_clear_lock)
+                atomic_set(&root->fs_info->mutually_exclusive_operation_running,
+                           0);
         mutex_unlock(&fs_info->balance_mutex);
         mutex_unlock(&fs_info->volume_mutex);
         mnt_drop_write_file(file);
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d2c0bccca607..33ca36b37a6a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2952,6 +2952,7 @@ static int balance_kthread(void *data)
                 ret = btrfs_balance(fs_info->balance_ctl, NULL);
         }
 
+        atomic_set(&fs_info->mutually_exclusive_operation_running, 0);
         mutex_unlock(&fs_info->balance_mutex);
         mutex_unlock(&fs_info->volume_mutex);
 
@@ -2974,6 +2975,7 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
                 return 0;
         }
 
+        WARN_ON(atomic_xchg(&fs_info->mutually_exclusive_operation_running, 1));
         tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
         if (IS_ERR(tsk))
                 return PTR_ERR(tsk);