1 files changed, 59 insertions, 2 deletions

diff --git a/mm/truncate.c b/mm/truncate.c
index 96d167372d89..f1e4d6052369 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -20,6 +20,7 @@
 #include <linux/buffer_head.h>  /* grr. try_to_release_page,
                                    do_invalidatepage */
 #include <linux/cleancache.h>
+#include <linux/rmap.h>
 #include "internal.h"
 
 static void clear_exceptional_entry(struct address_space *mapping,
@@ -714,17 +715,73 @@ EXPORT_SYMBOL(truncate_pagecache);
  * necessary) to @newsize. It will be typically be called from the filesystem's
  * setattr function when ATTR_SIZE is passed in.
  *
- * Must be called with inode_mutex held and before all filesystem specific
- * block truncation has been performed.
+ * Must be called with a lock serializing truncates and writes (generally
+ * i_mutex but e.g. xfs uses a different lock) and before all filesystem
+ * specific block truncation has been performed.
  */
 void truncate_setsize(struct inode *inode, loff_t newsize)
 {
+        loff_t oldsize = inode->i_size;
+
         i_size_write(inode, newsize);
+        if (newsize > oldsize)
+                pagecache_isize_extended(inode, oldsize, newsize);
         truncate_pagecache(inode, newsize);
 }
 EXPORT_SYMBOL(truncate_setsize);
 
 /**
+ * pagecache_isize_extended - update pagecache after extension of i_size
+ * @inode:      inode for which i_size was extended
+ * @from:       original inode size
+ * @to:         new inode size
+ *
+ * Handle extension of inode size either caused by extending truncate or by
+ * write starting after current i_size. We mark the page straddling current
+ * i_size RO so that page_mkwrite() is called on the nearest write access to
+ * the page.  This way filesystem can be sure that page_mkwrite() is called on
+ * the page before user writes to the page via mmap after the i_size has been
+ * changed.
+ *
+ * The function must be called after i_size is updated so that page fault
+ * coming after we unlock the page will already see the new i_size.
+ * The function must be called while we still hold i_mutex - this not only
+ * makes sure i_size is stable but also that userspace cannot observe new
+ * i_size value before we are prepared to store mmap writes at new inode size.
+ */
+void pagecache_isize_extended(struct inode *inode, loff_t from, loff_t to)
+{
+        int bsize = 1 << inode->i_blkbits;
+        loff_t rounded_from;
+        struct page *page;
+        pgoff_t index;
+
+        WARN_ON(to > inode->i_size);
+
+        if (from >= to || bsize == PAGE_CACHE_SIZE)
+                return;
+        /* Page straddling @from will not have any hole block created? */
+        rounded_from = round_up(from, bsize);
+        if (to <= rounded_from || !(rounded_from & (PAGE_CACHE_SIZE - 1)))
+                return;
+
+        index = from >> PAGE_CACHE_SHIFT;
+        page = find_lock_page(inode->i_mapping, index);
+        /* Page not cached? Nothing to do */
+        if (!page)
+                return;
+        /*
+         * See clear_page_dirty_for_io() for details why set_page_dirty()
+         * is needed.
+         */
+        if (page_mkclean(page))
+                set_page_dirty(page);
+        unlock_page(page);
+        page_cache_release(page);
+}
+EXPORT_SYMBOL(pagecache_isize_extended);
+
+/**
  * truncate_pagecache_range - unmap and remove pagecache that is hole-punched
  * @inode: inode
  * @lstart: offset of beginning of hole