du: handle sub-bind-mount cycles gracefully

This patch fixes the handling of sub-bind-mount cycles which are
incorrectly detected as the file system errors.  If you bind mount the
directory 'a' to its subdirectory 'a/b/c' and then run 'du a/b' you
will get the circular dependency warning even though nothing is wrong
with the file system.  This happens because the first directory that is
traversed twice in this case is not a bind mount but a child of bind
mount.  The solution is to traverse all the directories in the cycle
that fts detected and check whether they are not a (bind) mount.

* src/du.c (mount_point_in_fts_cycle): New function that checks whether
any of the directories in the cycle that fts detected is a mount point.
* src/du.c (process_file): Update the function to use the new function
that looks up all the directories in the fts cycle instead of only the
last one.
* tests/du/bind-mount-dir-cycle-v2.sh: New test case that exhibits the
described behavior.
* tests/local.mk: Reference the new root test.
* NEWS: Mention the bug fix.

1 files changed, 4 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 3a626563e..94e6d2529 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   dd supports more robust SIGINFO/SIGUSR1 handling for outputting statistics.
   Previously those signals may have inadvertently terminated the process.
 
+  du now silently ignores all directory cycles due to bind mounts.
+  Previously it would issue a warning and exit with a failure status.
+  [bug introduced in coreutils-8.1 and partially fixed in coreutils-8.23]
+
   chroot again calls chroot(DIR) and chdir("/"), even if DIR is "/".
   This handles separate bind mounted "/" trees, and environments
   depending on the implicit chdir("/").