File systems call dax_break_mapping() prior to reallocating file
system blocks to ensure the page is not undergoing any DMA or other
accesses. Generally this is needed when a file is truncated to ensure
that if a block is reallocated nothing is writing to it. However
filesystems currently don't call this when an FS DAX inode is evicted.

This can cause problems when the file system is unmounted as a page
can continue to be under going DMA or other remote access after
unmount. This means if the file system is remounted any truncate or
other operation which requires the underlying file system block to be
freed will not wait for the remote access to complete. Therefore a
busy block may be reallocated to a new file leading to corruption.

Signed-off-by: Alistair Popple <apopple@nvidia.com>

---

Changes for v5:

 - Don't wait for pages to be idle in non-DAX mappings
---
 fs/dax.c            | 29 +++++++++++++++++++++++++++++
 fs/ext4/inode.c     | 32 ++++++++++++++------------------
 fs/xfs/xfs_inode.c  |  9 +++++++++
 fs/xfs/xfs_inode.h  |  1 +
 fs/xfs/xfs_super.c  | 18 ++++++++++++++++++
 include/linux/dax.h |  2 ++
 6 files changed, 73 insertions(+), 18 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 7008a73..4e49cc4 100644
--- a/fs/dax.c
+++ b/fs/dax.c

@@ -883,6 +883,14 @@ static int wait_page_idle(struct page *page,
 				TASK_INTERRUPTIBLE, 0, 0, cb(inode));
 }
 
+static void wait_page_idle_uninterruptible(struct page *page,
+					void (cb)(struct inode *),
+					struct inode *inode)
+{
+	___wait_var_event(page, page_ref_count(page) == 1,
+			TASK_UNINTERRUPTIBLE, 0, 0, cb(inode));
+}
+
 /*
  * Unmaps the inode and waits for any DMA to complete prior to deleting the
  * DAX mapping entries for the range.

@@ -911,6 +919,27 @@ int dax_break_mapping(struct inode *inode, loff_t start, loff_t end,
 }
 EXPORT_SYMBOL_GPL(dax_break_mapping);
 
+void dax_break_mapping_uninterruptible(struct inode *inode,
+				void (cb)(struct inode *))
+{
+	struct page *page;
+
+	if (!dax_mapping(inode->i_mapping))
+		return;
+
+	do {
+		page = dax_layout_busy_page_range(inode->i_mapping, 0,
+						LLONG_MAX);
+		if (!page)
+			break;
+
+		wait_page_idle_uninterruptible(page, cb, inode);
+	} while (true);
+
+	dax_delete_mapping_range(inode->i_mapping, 0, LLONG_MAX);
+}
+EXPORT_SYMBOL_GPL(dax_break_mapping_uninterruptible);