ext4: prevent parallel resizers by atomic bit ops

Before this patch, parallel resizers are allowed and protected by a
mutex lock, actually, there is no need to support parallel resizer, so
this patch prevents parallel resizers by atmoic bit ops, like
lock_page() and unlock_page() do.

To do this, the patch removed the mutex lock s_resize_lock from struct
ext4_sb_info and added a unsigned long field named s_resize_flags
which inidicates if there is a resizer.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 8 insertions, 4 deletions

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 808c554e773f..f18bfe37aff8 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -202,8 +202,9 @@ setversion_out:
                 struct super_block *sb = inode->i_sb;
                 int err, err2=0;
 
-                if (!capable(CAP_SYS_RESOURCE))
-                        return -EPERM;
+                err = ext4_resize_begin(sb);
+                if (err)
+                        return err;
 
                 if (get_user(n_blocks_count, (__u32 __user *)arg))
                         return -EFAULT;
@@ -221,6 +222,7 @@ setversion_out:
                 if (err == 0)
                         err = err2;
                 mnt_drop_write(filp->f_path.mnt);
+                ext4_resize_end(sb);
 
                 return err;
         }
@@ -271,8 +273,9 @@ mext_out:
                 struct super_block *sb = inode->i_sb;
                 int err, err2=0;
 
-                if (!capable(CAP_SYS_RESOURCE))
-                        return -EPERM;
+                err = ext4_resize_begin(sb);
+                if (err)
+                        return err;
 
                 if (copy_from_user(&input, (struct ext4_new_group_input __user *)arg,
                                 sizeof(input)))
@@ -291,6 +294,7 @@ mext_out:
                 if (err == 0)
                         err = err2;
                 mnt_drop_write(filp->f_path.mnt);
+                ext4_resize_end(sb);
 
                 return err;
         }