3 files changed, 32 insertions, 24 deletions

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index cae65dc42bcc..22a20af4d785 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -61,6 +61,7 @@ extern struct file *shmem_file_setup(const char *name,
                                         loff_t size, unsigned long flags);
 extern int shmem_zero_setup(struct vm_area_struct *);
 extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
+extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
 extern int shmem_unuse(swp_entry_t entry, struct page *page);
 extern void mem_cgroup_get_shmem_target(struct inode *inode, pgoff_t pgoff,
                                         struct page **pagep, swp_entry_t *ent);
diff --git a/mm/shmem.c b/mm/shmem.c
index d221a1cfd7b1..f1714758ea96 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -539,7 +539,7 @@ static void shmem_free_pages(struct list_head *next)
         } while (next);
 }
 
-static void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)
+void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)
 {
         struct shmem_inode_info *info = SHMEM_I(inode);
         unsigned long idx;
@@ -562,6 +562,8 @@ static void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)
         spinlock_t *punch_lock;
         unsigned long upper_limit;
 
+        truncate_inode_pages_range(inode->i_mapping, start, end);
+
         inode->i_ctime = inode->i_mtime = CURRENT_TIME;
         idx = (start + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
         if (idx >= info->next_index)
@@ -738,16 +740,8 @@ done2:
                  * lowered next_index.  Also, though shmem_getpage checks
                  * i_size before adding to cache, no recheck after: so fix the
                  * narrow window there too.
-                 *
-                 * Recalling truncate_inode_pages_range and unmap_mapping_range
-                 * every time for punch_hole (which never got a chance to clear
-                 * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
-                 * yet hardly ever necessary: try to optimize them out later.
                  */
                 truncate_inode_pages_range(inode->i_mapping, start, end);
-                if (punch_hole)
-                        unmap_mapping_range(inode->i_mapping, start,
-                                                        end - start, 1);
         }
 
         spin_lock(&info->lock);
@@ -766,22 +760,23 @@ done2:
                 shmem_free_pages(pages_to_free.next);
         }
 }
+EXPORT_SYMBOL_GPL(shmem_truncate_range);
 
-static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
+static int shmem_setattr(struct dentry *dentry, struct iattr *attr)
 {
         struct inode *inode = dentry->d_inode;
-        loff_t newsize = attr->ia_size;
         int error;
 
         error = inode_change_ok(inode, attr);
         if (error)
                 return error;
 
-        if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)
-                                        && newsize != inode->i_size) {
+        if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
+                loff_t oldsize = inode->i_size;
+                loff_t newsize = attr->ia_size;
                 struct page *page = NULL;
 
-                if (newsize < inode->i_size) {
+                if (newsize < oldsize) {
                         /*
                          * If truncating down to a partial page, then
                          * if that page is already allocated, hold it
@@ -810,12 +805,19 @@ static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
                                 spin_unlock(&info->lock);
                         }
                 }
-
-                /* XXX(truncate): truncate_setsize should be called last */
-                truncate_setsize(inode, newsize);
+                if (newsize != oldsize) {
+                        i_size_write(inode, newsize);
+                        inode->i_ctime = inode->i_mtime = CURRENT_TIME;
+                }
+                if (newsize < oldsize) {
+                        loff_t holebegin = round_up(newsize, PAGE_SIZE);
+                        unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
+                        shmem_truncate_range(inode, newsize, (loff_t)-1);
+                        /* unmap again to remove racily COWed private pages */
+                        unmap_mapping_range(inode->i_mapping, holebegin, 0, 1);
+                }
                 if (page)
                         page_cache_release(page);
-                shmem_truncate_range(inode, newsize, (loff_t)-1);
         }
 
         setattr_copy(inode, attr);
@@ -832,7 +834,6 @@ static void shmem_evict_inode(struct inode *inode)
         struct shmem_xattr *xattr, *nxattr;
 
         if (inode->i_mapping->a_ops == &shmem_aops) {
-                truncate_inode_pages(inode->i_mapping, 0);
                 shmem_unacct_size(info->flags, inode->i_size);
                 inode->i_size = 0;
                 shmem_truncate_range(inode, 0, (loff_t)-1);
@@ -2706,7 +2707,7 @@ static const struct file_operations shmem_file_operations = {
 };
 
 static const struct inode_operations shmem_inode_operations = {
-        .setattr        = shmem_notify_change,
+        .setattr        = shmem_setattr,
         .truncate_range = shmem_truncate_range,
 #ifdef CONFIG_TMPFS_XATTR
         .setxattr       = shmem_setxattr,
@@ -2739,7 +2740,7 @@ static const struct inode_operations shmem_dir_inode_operations = {
         .removexattr    = shmem_removexattr,
 #endif
 #ifdef CONFIG_TMPFS_POSIX_ACL
-        .setattr        = shmem_notify_change,
+        .setattr        = shmem_setattr,
         .check_acl      = generic_check_acl,
 #endif
 };
@@ -2752,7 +2753,7 @@ static const struct inode_operations shmem_special_inode_operations = {
         .removexattr    = shmem_removexattr,
 #endif
 #ifdef CONFIG_TMPFS_POSIX_ACL
-        .setattr        = shmem_notify_change,
+        .setattr        = shmem_setattr,
         .check_acl      = generic_check_acl,
 #endif
 };
@@ -2908,6 +2909,12 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)
         return 0;
 }
 
+void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)
+{
+        truncate_inode_pages_range(inode->i_mapping, start, end);
+}
+EXPORT_SYMBOL_GPL(shmem_truncate_range);
+
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
 /**
  * mem_cgroup_get_shmem_target - find a page or entry assigned to the shmem file
diff --git a/mm/truncate.c b/mm/truncate.c
index 5b4c3a4847e9..29a9b8a5a31a 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -619,9 +619,9 @@ int vmtruncate_range(struct inode *inode, loff_t offset, loff_t end)
         mutex_lock(&inode->i_mutex);
         down_write(&inode->i_alloc_sem);
         unmap_mapping_range(mapping, offset, (end - offset), 1);
-        truncate_inode_pages_range(mapping, offset, end);
-        unmap_mapping_range(mapping, offset, (end - offset), 1);
         inode->i_op->truncate_range(inode, offset, end);
+        /* unmap again to remove racily COWed private pages */
+        unmap_mapping_range(mapping, offset, (end - offset), 1);
         up_write(&inode->i_alloc_sem);
         mutex_unlock(&inode->i_mutex);