1 files changed, 41 insertions, 44 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index 179f1c33ea57..672b187def62 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 - generic llseek implementation for regular files
  * @file:       file structure to seek on
  * @offset:     file offset to seek to
  * @origin:     type of seek
  *
- * Updates the file offset to the value specified by @offset and @origin.
- * Locking must be provided by the caller.
+ * This is a generic implemenation of ->llseek usable for all normal local
+ * filesystems.  It just updates the file offset to the value specified by
+ * @offset and @origin under i_mutex.
+ *
+ * Synchronization:
+ * SEEK_SET is 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.
+ * SEEK_END
  */
 loff_t
-generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
+generic_file_llseek(struct file *file, loff_t offset, int origin)
 {
         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,
+                                       inode->i_sb->s_maxbytes);
+                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:
@@ -77,46 +107,13 @@ 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;
-}
-EXPORT_SYMBOL(generic_file_llseek_unlocked);
-
-/**
- * generic_file_llseek - generic llseek implementation for regular files
- * @file:       file structure to seek on
- * @offset:     file offset to seek to
- * @origin:     type of seek
- *
- * This is a generic implemenation of ->llseek useable for all normal local
- * filesystems.  It just updates the file offset to the value specified by
- * @offset and @origin under i_mutex.
- */
-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);
-
-        return rval;
+        return lseek_execute(file, inode, offset, inode->i_sb->s_maxbytes);
 }
 EXPORT_SYMBOL(generic_file_llseek);