[PATCH 6/6] xfs: xfs_filemap_pmd_fault treats read faults as write faults

Dave Chinner
2015-10-19T03:27:40Z

From: Dave Chinner <dchinner@redhat.com>

The code initially committed didn't have the same checks for write
faults as the dax_pmd_fault code and hence treats all faults as
write faults. We can get read faults through this path because they
is no pmd_mkwrite path for write faults similar to the normal page
fault path. Hence we need to ensure that we only do c/mtime updates
on write faults, and freeze protection is unnecessary for read
faults.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_file.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index e7cf9ec..0045b0a 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1482,7 +1482,7 @@ xfs_file_llseek(
*
* mmap_sem (MM)
* sb_start_pagefault(vfs, freeze)
- * i_mmap_lock (XFS - truncate serialisation)
+ * i_mmaplock (XFS - truncate serialisation)
* page_lock (MM)
* i_lock (XFS - extent map serialisation)
*/
@@ -1550,6 +1550,13 @@ xfs_filemap_fault(
return ret;
}

+/*
+ * Similar to xfs_filemap_fault(), the DAX fault path can call into here on
+ * both read and write faults. Hence we need to handle both cases. There is no
+ * ->pmd_mkwrite callout for huge pages, so we have a single function here to
+ * handle both cases here. @flags carries the information on the type of fault
+ * occuring.
+ */
STATIC int
xfs_filemap_pmd_fault(
struct vm_area_struct *vma,
@@ -1566,13 +1573,18 @@ xfs_filemap_pmd_fault(

trace_xfs_filemap_pmd_fault(ip);

- sb_start_pagefault(inode->i_sb);
- file_update_time(vma->vm_file);
+ if (flags & FAULT_FLAG_WRITE) {
+ sb_start_pagefault(inode->i_sb);
+ file_update_time(vma->vm_file);
+ }
+
xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
ret = __dax_pmd_fault(vma, addr, pmd, flags, xfs_get_blocks_dax_fault,
NULL);
xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
- sb_end_pagefault(inode->i_sb);
+
+ if (flags & FAULT_FLAG_WRITE)
+ sb_end_pagefault(inode->i_sb);

return ret;
}
--
2.5.0