1 files changed, 45 insertions, 29 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index 179f1c3..dfd1257 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -35,23 +35,45 @@ static inline int unsigned_offsets(struct file *file)
 	return file->f_mode & FMODE_UNSIGNED_OFFSET;
 }
 
+static loff_t lseek_execute(struct file *file, struct inode *inode,
+		loff_t offset, loff_t maxsize)
+{
+	if (offset < 0 && !unsigned_offsets(file))
+		return -EINVAL;
+	if (offset > maxsize)
+		return -EINVAL;
+
+	if (offset != file->f_pos) {
+		file->f_pos = offset;
+		file->f_version = 0;
+	}
+	return offset;
+}
+
 /**
- * generic_file_llseek_unlocked - lockless generic llseek implementation
+ * generic_file_llseek_size - generic llseek implementation for regular files
  * @file:	file structure to seek on
  * @offset:	file offset to seek to
  * @origin:	type of seek
+ * @size:	max size of file system
+ *
+ * This is a variant of generic_file_llseek that allows passing in a custom
+ * file size.
  *
- * Updates the file offset to the value specified by @offset and @origin.
- * Locking must be provided by the caller.
+ * Synchronization:
+ * SEEK_SET and SEEK_END are unsynchronized (but atomic on 64bit platforms)
+ * SEEK_CUR is synchronized against other SEEK_CURs, but not read/writes.
+ * read/writes behave like SEEK_SET against seeks.
  */
 loff_t
-generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
+generic_file_llseek_size(struct file *file, loff_t offset, int origin,
+		loff_t maxsize)
 {
 	struct inode *inode = file->f_mapping->host;
 
 	switch (origin) {
 	case SEEK_END:
-		offset += inode->i_size;
+		offset += i_size_read(inode);
 		break;
 	case SEEK_CUR:
 		/*
@@ -62,14 +84,22 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
 		 */
 		if (offset == 0)
 			return file->f_pos;
-		offset += file->f_pos;
-		break;
+		/*
+		 * f_lock protects against read/modify/write race with other
+		 * SEEK_CURs. Note that parallel writes and reads behave
+		 * like SEEK_SET.
+		 */
+		spin_lock(&file->f_lock);
+		offset = lseek_execute(file, inode, file->f_pos + offset,
+				       maxsize);
+		spin_unlock(&file->f_lock);
+		return offset;
 	case SEEK_DATA:
 		/*
 		 * In the generic case the entire file is data, so as long as
 		 * offset isn't at the end of the file then the offset is data.
 		 */
-		if (offset >= inode->i_size)
+		if (offset >= i_size_read(inode))
 			return -ENXIO;
 		break;
 	case SEEK_HOLE:
@@ -77,26 +107,15 @@ generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
 		 * There is a virtual hole at the end of the file, so as long as
 		 * offset isn't i_size or larger, return i_size.
 		 */
-		if (offset >= inode->i_size)
+		if (offset >= i_size_read(inode))
 			return -ENXIO;
-		offset = inode->i_size;
+		offset = i_size_read(inode);
 		break;
 	}
 
-	if (offset < 0 && !unsigned_offsets(file))
-		return -EINVAL;
-	if (offset > inode->i_sb->s_maxbytes)
-		return -EINVAL;
-
-	/* Special lock needed here? */
-	if (offset != file->f_pos) {
-		file->f_pos = offset;
-		file->f_version = 0;
-	}
-
-	return offset;
+	return lseek_execute(file, inode, offset, maxsize);
 }
-EXPORT_SYMBOL(generic_file_llseek_unlocked);
+EXPORT_SYMBOL(generic_file_llseek_size);
 
 /**
  * generic_file_llseek - generic llseek implementation for regular files
@@ -110,13 +129,10 @@ EXPORT_SYMBOL(generic_file_llseek_unlocked);
  */
 loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
 {
-	loff_t rval;
-
-	mutex_lock(&file->f_dentry->d_inode->i_mutex);
-	rval = generic_file_llseek_unlocked(file, offset, origin);
-	mutex_unlock(&file->f_dentry->d_inode->i_mutex);
+	struct inode *inode = file->f_mapping->host;
 
-	return rval;
+	return generic_file_llseek_size(file, offset, origin,
+					inode->i_sb->s_maxbytes);
 }
 EXPORT_SYMBOL(generic_file_llseek);