ceph: don't freeze during write page faults

Prevent freezing operations during write page faults. This is good
practice for most filesystems, but especially for ceph since we're
monkeying with the signal table here.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/addr.c

@@ -1548,6 +1548,7 @@ static vm_fault_t ceph_page_mkwrite(struct vm_fault *vmf)
 	if (!prealloc_cf)
 		return VM_FAULT_OOM;
 
+	sb_start_pagefault(inode->i_sb);
 	ceph_block_sigs(&oldset);
 
 	if (ci->i_inline_version != CEPH_INLINE_NONE) {
@@ -1622,6 +1623,7 @@ static vm_fault_t ceph_page_mkwrite(struct vm_fault *vmf)
 	ceph_put_cap_refs(ci, got);
 out_free:
 	ceph_restore_sigs(&oldset);
+	sb_end_pagefault(inode->i_sb);
 	ceph_free_cap_flush(prealloc_cf);
 	if (err < 0)
 		ret = vmf_error(err);