Merge tag 'v4.13-rc1' into fixes

The fixes branch is based off a random pre-rc1 commit, because we had
some fixes that needed to go in before rc1 was released.

However we now need to fix some code that went in after that point, but
before rc1, so merge rc1 to get that code into fixes so we can fix it!

1 files changed, 23 insertions, 1 deletions

diff --git a/fs/nfsd/nfsfh.h b/fs/nfsd/nfsfh.h
index f84fe6bf9aee..e47cf6c2ac28 100644
--- a/fs/nfsd/nfsfh.h
+++ b/fs/nfsd/nfsfh.h
@@ -241,6 +241,28 @@ fh_clear_wcc(struct svc_fh *fhp)
 }
 
 /*
+ * We could use i_version alone as the change attribute.  However,
+ * i_version can go backwards after a reboot.  On its own that doesn't
+ * necessarily cause a problem, but if i_version goes backwards and then
+ * is incremented again it could reuse a value that was previously used
+ * before boot, and a client who queried the two values might
+ * incorrectly assume nothing changed.
+ *
+ * By using both ctime and the i_version counter we guarantee that as
+ * long as time doesn't go backwards we never reuse an old value.
+ */
+static inline u64 nfsd4_change_attribute(struct inode *inode)
+{
+	u64 chattr;
+
+	chattr =  inode->i_ctime.tv_sec;
+	chattr <<= 30;
+	chattr += inode->i_ctime.tv_nsec;
+	chattr += inode->i_version;
+	return chattr;
+}
+
+/*
  * Fill in the pre_op attr for the wcc data
  */
 static inline void
@@ -253,7 +275,7 @@ fill_pre_wcc(struct svc_fh *fhp)
 		fhp->fh_pre_mtime = inode->i_mtime;
 		fhp->fh_pre_ctime = inode->i_ctime;
 		fhp->fh_pre_size  = inode->i_size;
-		fhp->fh_pre_change = inode->i_version;
+		fhp->fh_pre_change = nfsd4_change_attribute(inode);
 		fhp->fh_pre_saved = true;
 	}
 }