ext4: close race between direct IO and ext4_break_layouts()

If the refcount of a page is lowered between the time that it is returned
by dax_busy_page() and when the refcount is again checked in
ext4_break_layouts() => ___wait_var_event(), the waiting function
ext4_wait_dax_page() will never be called.  This means that
ext4_break_layouts() will still have 'retry' set to false, so we'll stop
looping and never check the refcount of other pages in this inode.

Instead, always continue looping as long as dax_layout_busy_page() gives us
a page which it found with an elevated refcount.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 694f3136420625fb5e3b31623035e6b6112fa75a..723058bfe43babbe582fa8f070582291dbaf90e0 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4195,9 +4195,8 @@ int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
        return 0;
 }
 
-static void ext4_wait_dax_page(struct ext4_inode_info *ei, bool *did_unlock)
+static void ext4_wait_dax_page(struct ext4_inode_info *ei)
 {
-       *did_unlock = true;
        up_write(&ei->i_mmap_sem);
        schedule();
        down_write(&ei->i_mmap_sem);
@@ -4207,14 +4206,12 @@ int ext4_break_layouts(struct inode *inode)
 {
        struct ext4_inode_info *ei = EXT4_I(inode);
        struct page *page;
-       bool retry;
        int error;
 
        if (WARN_ON_ONCE(!rwsem_is_locked(&ei->i_mmap_sem)))
                return -EINVAL;
 
        do {
-               retry = false;
                page = dax_layout_busy_page(inode->i_mapping);
                if (!page)
                        return 0;
@@ -4222,8 +4219,8 @@ int ext4_break_layouts(struct inode *inode)
                error = ___wait_var_event(&page->_refcount,
                                atomic_read(&page->_refcount) == 1,
                                TASK_INTERRUPTIBLE, 0, 0,
-                               ext4_wait_dax_page(ei, &retry));
-       } while (error == 0 && retry);
+                               ext4_wait_dax_page(ei));
+       } while (error == 0);
 
        return error;
 }