The patch below does not apply to the 4.18-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b1f382178d150f256c1cf95b9341fda6eb764459 Mon Sep 17 00:00:00 2001

From: Ross Zwisler zwisler@kernel.org Date: Tue, 11 Sep 2018 13:31:16 -0400 Subject: [PATCH] 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 694f31364206..723058bfe43b 100644 --- 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; }