commit 6de46ad743f5ee093e41eb8eff739509fffd44a3
Author: Erez_Zadok <[EMAIL PROTECTED]>
Date: Sat Jul 14 03:36:15 2007 -0400
Unionfs: rewrite do_unionfs_readpage to use vfs_read (bugfix)
In do_unionfs_readpage, we used to call the lower file system's ->readpage.
However, some file systems (e.g., tmpfs) don't implement ->readpage, causing
a NULL pointer dereference under certain conditions, especially under severe
memory pressure. This patch reimplements do_unionfs_readpage using
vfs_read, which makes the code simpler and more reliable, as we depend on
the VFS to do most of the hard work (even if this implementation might be a
bit slower).
This fix also makes sense because it makes the mmap code in unionfs more
symmetric with unionfs_commit_write --- which uses vfs_write().
Signed-off-by: Erez Zadok <[EMAIL PROTECTED]>
diff --git a/fs/unionfs/mmap.c b/fs/unionfs/mmap.c
index 6f72149..2d8fe77 100644
--- a/fs/unionfs/mmap.c
+++ b/fs/unionfs/mmap.c
@@ -114,85 +114,53 @@ out:
static int unionfs_do_readpage(struct file *file, struct page *page)
{
int err = -EIO;
- struct dentry *dentry;
- struct file *lower_file = NULL;
- struct inode *inode, *lower_inode;
- char *page_data;
- struct page *lower_page;
- char *lower_page_data;
+ struct file *lower_file;
+ struct inode *inode;
+ mm_segment_t old_fs;
+ char *page_data = NULL;
+ loff_t offset;
- dentry = file->f_path.dentry;
if (UNIONFS_F(file) == NULL) {
err = -ENOENT;
- goto out_err;
+ goto out;
}
lower_file = unionfs_lower_file(file);
- inode = dentry->d_inode;
- lower_inode = unionfs_lower_inode(inode);
+ /* FIXME: is this assertion right here? */
+ BUG_ON(lower_file == NULL);
- lower_page = NULL;
-
- /* find lower page (returns a locked page) */
- lower_page = read_cache_page(lower_inode->i_mapping,
- page->index,
- (filler_t *) lower_inode->i_mapping->
- a_ops->readpage, (void *)lower_file);
-
- if (IS_ERR(lower_page)) {
- err = PTR_ERR(lower_page);
- lower_page = NULL;
- goto out_release;
- }
+ inode = file->f_path.dentry->d_inode;
+ page_data = (char *) kmap(page);
/*
- * wait for the page data to show up
- * (signaled by readpage as unlocking the page)
+ * Use vfs_read because some lower file systems don't have a
+ * readpage method, and some file systems (esp. distributed ones)
+ * don't like their pages to be accessed directly. Using vfs_read
+ * may be a little slower, but a lot safer, as the VFS does a lot of
+ * the necessary magic for us.
*/
- wait_on_page_locked(lower_page);
- if (!PageUptodate(lower_page)) {
- /*
- * call readpage() again if we returned from wait_on_page
- * with a page that's not up-to-date; that can happen when a
- * partial page has a few buffers which are ok, but not the
- * whole page.
- */
- lock_page(lower_page);
- err = lower_inode->i_mapping->a_ops->readpage(lower_file,
- lower_page);
- if (err) {
- lower_page = NULL;
- goto out_release;
- }
-
- wait_on_page_locked(lower_page);
- if (!PageUptodate(lower_page)) {
- err = -EIO;
- goto out_release;
- }
- }
-
- /* map pages, get their addresses */
- page_data = (char *)kmap(page);
- lower_page_data = (char *)kmap(lower_page);
+ offset = lower_file->f_pos = (page->index << PAGE_CACHE_SHIFT);
+ old_fs = get_fs();
+ set_fs(KERNEL_DS);
+ err = vfs_read(lower_file, page_data, PAGE_CACHE_SIZE,
+ &lower_file->f_pos);
+ set_fs(old_fs);
- memcpy(page_data, lower_page_data, PAGE_CACHE_SIZE);
+ kunmap(page);
+ if (err < 0)
+ goto out;
err = 0;
- kunmap(lower_page);
- kunmap(page);
-
-out_release:
- if (lower_page)
- page_cache_release(lower_page); /* undo read_cache_page */
+ /* if vfs_read succeeded above, sync up our times */
+ unionfs_copy_attr_times(inode);
+out:
if (err == 0)
SetPageUptodate(page);
else
ClearPageUptodate(page);
-out_err:
return err;
}
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