1 files changed, 23 insertions, 1 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index f6ad8f9b8fa5..b0675bfe8207 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2331,6 +2331,9 @@ EXPORT_SYMBOL(block_commit_write);
  * page lock we can determine safely if the page is beyond EOF. If it is not
  * beyond EOF, then the page is guaranteed safe against truncation until we
  * unlock the page.
+ *
+ * Direct callers of this function should call vfs_check_frozen() so that page
+ * fault does not busyloop until the fs is thawed.
  */
 int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
                          get_block_t get_block)
@@ -2362,6 +2365,18 @@ int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 
         if (unlikely(ret < 0))
                 goto out_unlock;
+        /*
+         * Freezing in progress? We check after the page is marked dirty and
+         * with page lock held so if the test here fails, we are sure freezing
+         * code will wait during syncing until the page fault is done - at that
+         * point page will be dirty and unlocked so freezing code will write it
+         * and writeprotect it again.
+         */
+        set_page_dirty(page);
+        if (inode->i_sb->s_frozen != SB_UNFROZEN) {
+                ret = -EAGAIN;
+                goto out_unlock;
+        }
         return 0;
 out_unlock:
         unlock_page(page);
@@ -2372,8 +2387,15 @@ EXPORT_SYMBOL(__block_page_mkwrite);
 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
                    get_block_t get_block)
 {
-        int ret = __block_page_mkwrite(vma, vmf, get_block);
+        int ret;
+        struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
 
+        /*
+         * This check is racy but catches the common case. The check in
+         * __block_page_mkwrite() is reliable.
+         */
+        vfs_check_frozen(sb, SB_FREEZE_WRITE);
+        ret = __block_page_mkwrite(vma, vmf, get_block);
         return block_page_mkwrite_return(ret);
 }
 EXPORT_SYMBOL(block_page_mkwrite);