[PATCH 5/6] xfs: add ->pfn_mkwrite support for DAX

Dave Chinner
2015-10-19T03:27:42Z

From: Dave Chinner <dchinner@redhat.com>

->pfn_mkwrite support is needed so that when a page with allocated
backing store takes a write fault we can check that the fault has
not raced with a truncate and is pointing to a region beyond the
current end of file.

This also allows us to update the timestamp on the inode, too, which
fixes a generic/080 failure.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_file.c | 35 +++++++++++++++++++++++++++++++++++
fs/xfs/xfs_trace.h | 1 +
2 files changed, 36 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 403151a..e7cf9ec 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1577,11 +1577,46 @@ xfs_filemap_pmd_fault(
return ret;
}

+/*
+ * pfn_mkwrite was originally inteneded to ensure we capture time stamp
+ * updates on write faults. In reality, it's need to serialise against
+ * truncate similar to page_mkwrite. Hence we open-code dax_pfn_mkwrite()
+ * here and cycle the XFS_MMAPLOCK_SHARED to ensure we serialise the fault
+ * barrier in place.
+ */
+static int
+xfs_filemap_pfn_mkwrite(
+ struct vm_area_struct *vma,
+ struct vm_fault *vmf)
+{
+
+ struct inode *inode = file_inode(vma->vm_file);
+ struct xfs_inode *ip = XFS_I(inode);
+ int ret = VM_FAULT_NOPAGE;
+ loff_t size;
+
+ trace_xfs_filemap_pfn_mkwrite(ip);
+
+ sb_start_pagefault(inode->i_sb);
+ file_update_time(vma->vm_file);
+
+ /* check if the faulting page hasn't raced with truncate */
+ xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
+ size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ if (vmf->pgoff >= size)
+ ret = VM_FAULT_SIGBUS;
+ xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
+ sb_end_pagefault(inode->i_sb);
+ return ret;
+
+}
+
static const struct vm_operations_struct xfs_file_vm_ops = {
.fault = xfs_filemap_fault,
.pmd_fault = xfs_filemap_pmd_fault,
.map_pages = filemap_map_pages,
.page_mkwrite = xfs_filemap_page_mkwrite,
+ .pfn_mkwrite = xfs_filemap_pfn_mkwrite,
};

STATIC int
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index 957f5cc..877079eb 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -689,6 +689,7 @@ DEFINE_INODE_EVENT(xfs_inode_free_eofblocks_invalid);
DEFINE_INODE_EVENT(xfs_filemap_fault);
DEFINE_INODE_EVENT(xfs_filemap_pmd_fault);
DEFINE_INODE_EVENT(xfs_filemap_page_mkwrite);
+DEFINE_INODE_EVENT(xfs_filemap_pfn_mkwrite);

DECLARE_EVENT_CLASS(xfs_iref_class,
TP_PROTO(struct xfs_inode *ip, unsigned long caller_ip),
--
2.5.0