geo-rep: Fix symlink rename syncing issue

Problem:
   Geo-rep sometimes fails to sync the rename of symlink
if the I/O is as follows

  1. touch file1
  2. ln -s "./file1" sym_400
  3. mv sym_400 renamed_sym_400
  4. mkdir sym_400

 The file 'renamed_sym_400' failed to sync to slave

Cause:
  Assume there are three distribute subvolume (brick1, brick2, brick3).
  The changelogs are recorded as follows for above I/O pattern.
  Note that the MKDIR is recorded on all bricks.

  1. brick1:
     -------

     CREATE file1
     SYMLINK sym_400
     RENAME sym_400 renamed_sym_400
     MKDIR sym_400

  2. brick2:
     -------

     MKDIR sym_400

  3. brick3:
     -------

     MKDIR sym_400

  The operations on 'brick1' should be processed sequentially. But
  since MKDIR is recorded on all the bricks, The brick 'brick2/brick3'
  processed MKDIR first before 'brick1' causing out of order syncing
  and created directory sym_400 first.

  Now 'brick1' processed it's changelog.

     CREATE file1 -> succeeds
     SYMLINK sym_400 -> No longer present in master. Ignored
     RENAME sym_400 renamed_sym_400
            While processing RENAME, if source('sym_400') doesn't
            present, destination('renamed_sym_400') is created. But
            geo-rep stats the name 'sym_400' to confirm source file's
            presence. In this race, since source name 'sym_400' is
            present as directory, it doesn't create destination.
            Hence RENAME is ignored.

Fix:
  The fix is not rely only on stat of source name during RENAME.
  It should stat the name and if the name is present, gfid should
  be same. Only then it can conclude the presence of source.

Backport of:
 > BUG: 1600405
 > Change-Id: I9fbec4f13ca6a182798a7f81b356fe2003aff969
 > Signed-off-by: Kotresh HR <khiremat@redhat.com>

fixes: bz#1611113
Change-Id: I9fbec4f13ca6a182798a7f81b356fe2003aff969
Signed-off-by: Kotresh HR <khiremat@redhat.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/geo-replication/syncdaemon/resource.py b/geo-replication/syncdaemon/resource.py
index e261812f39f..a22dc43c859 100644
--- a/geo-replication/syncdaemon/resource.py
+++ b/geo-replication/syncdaemon/resource.py
@@ -621,8 +621,14 @@ class Server(object):
                     collect_failure(e, EEXIST)
             elif op == 'RENAME':
                 en = e['entry1']
-                st = lstat(entry)
-                if isinstance(st, int):
+                # The matching disk gfid check validates two things
+                #  1. Validates name is present, return false otherwise
+                #  2. Validates gfid is same, returns false otherwise
+                # So both validations are necessary to decide src doesn't
+                # exist. We can't rely on only gfid stat as hardlink could
+                # be present and we can't rely only on name as name could
+                # exist with differnt gfid.
+                if not matching_disk_gfid(gfid, entry):
                     if e['stat'] and not stat.S_ISDIR(e['stat']['mode']):
                         if stat.S_ISLNK(e['stat']['mode']) and \
                            e['link'] is not None:
@@ -646,6 +652,7 @@ class Server(object):
                                                     [ENOENT, EEXIST], [ESTALE])
                                 collect_failure(e, cmd_ret)
                 else:
+                    st = lstat(entry)
                     st1 = lstat(en)
                     if isinstance(st1, int):
                         rename_with_disk_gfid_confirmation(gfid, entry, en)