[PATCH RFC 09/10] fs/xfs: Fail truncate if pages are GUP pinned

[ira . weiny]

From: Ira Weiny <ira.weiny@xxxxxxxxx>

If pages are actively gup pinned fail the truncate operation.  To
support an application who wishes to removing a pin upon SIGIO reception
we must change the order of breaking layout leases with respect to DAX
layout leases.

Check for a GUP pin on the page being truncated and return ETXTBSY if it
is GUP pinned.

Change the order of XFS break leased layouts and break DAX layouts.

Select EXPORT_BLOCK_OPS for FS_DAX to ensure that
xfs_break_lease_layouts() is defined for FS_DAX as well as pNFS.

Update comment for xfs_break_lease_layouts()

Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
---
 fs/Kconfig        |  1 +
 fs/xfs/xfs_file.c |  8 ++++++--
 fs/xfs/xfs_pnfs.c | 14 +++++++-------
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/fs/Kconfig b/fs/Kconfig
index f1046cf6ad85..c54b0b88abbf 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -49,6 +49,7 @@ config FS_DAX
 	select DEV_PAGEMAP_OPS if (ZONE_DEVICE && !FS_DAX_LIMITED)
 	select FS_IOMAP
 	select DAX
+	select EXPORTFS_BLOCK_OPS
 	help
 	  Direct Access (DAX) can be used on memory-backed block devices.
 	  If the block device supports DAX and the filesystem supports DAX,
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 350eb5546d36..1dc61c98f7cd 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -756,6 +756,9 @@ xfs_break_dax_layouts(
 	if (!page)
 		return 0;
 
+	if (page_gup_pinned(page))
+		return -ETXTBSY;
+
 	*retry = true;
 	return ___wait_var_event(&page->_refcount,
 			atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE,
@@ -779,10 +782,11 @@ xfs_break_layouts(
 		retry = false;
 		switch (reason) {
 		case BREAK_UNMAP:
-			error = xfs_break_dax_layouts(inode, &retry, off, len);
+			error = xfs_break_leased_layouts(inode, iolock, &retry);
 			if (error || retry)
 				break;
-			/* fall through */
+			error = xfs_break_dax_layouts(inode, &retry, off, len);
+			break;
 		case BREAK_WRITE:
 			error = xfs_break_leased_layouts(inode, iolock, &retry);
 			break;
diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
index bde2c9f56a46..e70d24d12cbf 100644
--- a/fs/xfs/xfs_pnfs.c
+++ b/fs/xfs/xfs_pnfs.c
@@ -21,14 +21,14 @@
 #include "xfs_pnfs.h"
 
 /*
- * Ensure that we do not have any outstanding pNFS layouts that can be used by
- * clients to directly read from or write to this inode.  This must be called
- * before every operation that can remove blocks from the extent map.
- * Additionally we call it during the write operation, where aren't concerned
- * about exposing unallocated blocks but just want to provide basic
+ * Ensure that we do not have any outstanding pNFS or longterm GUP layouts that
+ * can be used by clients to directly read from or write to this inode.  This
+ * must be called before every operation that can remove blocks from the extent
+ * map.  Additionally we call it during the write operation, where aren't
+ * concerned about exposing unallocated blocks but just want to provide basic
  * synchronization between a local writer and pNFS clients.  mmap writes would
- * also benefit from this sort of synchronization, but due to the tricky locking
- * rules in the page fault path we don't bother.
+ * also benefit from this sort of synchronization, but due to the tricky
+ * locking rules in the page fault path we don't bother.
  */
 int
 xfs_break_leased_layouts(
-- 
2.20.1