ext4: fix lost truncate due to race with writeback

[~andy/linux] / fs / ext4 / ext4.h

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 58dede76f75ff5bcb89ac510e1367be9070fa14b..3dbc56eb4849d624ad38e768ff350ea1af463af0 100644 (file)
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2432,16 +2432,32 @@ do {                                                            \
 #define EXT4_FREECLUSTERS_WATERMARK 0
 #endif
 
+/* Update i_disksize. Requires i_mutex to avoid races with truncate */
 static inline void ext4_update_i_disksize(struct inode *inode, loff_t newsize)
 {
-       /*
-        * XXX: replace with spinlock if seen contended -bzzz
-        */
+       WARN_ON_ONCE(S_ISREG(inode->i_mode) &&
+                    !mutex_is_locked(&inode->i_mutex));
+       down_write(&EXT4_I(inode)->i_data_sem);
+       if (newsize > EXT4_I(inode)->i_disksize)
+               EXT4_I(inode)->i_disksize = newsize;
+       up_write(&EXT4_I(inode)->i_data_sem);
+}
+
+/*
+ * Update i_disksize after writeback has been started. Races with truncate
+ * are avoided by checking i_size under i_data_sem.
+ */
+static inline void ext4_wb_update_i_disksize(struct inode *inode, loff_t newsize)
+{
+       loff_t i_size;
+
        down_write(&EXT4_I(inode)->i_data_sem);
+       i_size = i_size_read(inode);
+       if (newsize > i_size)
+               newsize = i_size;
        if (newsize > EXT4_I(inode)->i_disksize)
                EXT4_I(inode)->i_disksize = newsize;
        up_write(&EXT4_I(inode)->i_data_sem);
-       return ;
 }
 
 struct ext4_group_info {