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Commit b1f38217 authored by Ross Zwisler's avatar Ross Zwisler Committed by Theodore Ts'o
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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: default avatarRoss Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
parent 5f8c1093

fs/ext4/inode.c

+3 −6
Original line number Diff line number Diff line
@@ -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;

}