[gvfs] metadata: Force tree re-read after successful flush

[Tomas Bzatek <tbzatek src gnome org>]

commit 6b12c3d7b33c87a7fea228106f39ecf2a3e0f310
Author: Tomas Bzatek <tbzatek redhat com>
Date:   Mon May 13 17:39:26 2013 +0200

    metadata: Force tree re-read after successful flush
    
    Once we flush the journal and write new tree file we need to re-read
    it to refresh internal data structures (and mmap data from the right
    file). We originally left this work on meta_tree_refresh_locked() and
    meta_tree_needs_rereading() respectively where we checked the rotated
    bit.
    
    In detail, metabuilder wrote a new temp tree file, then explicitly opened
    the current (old) one, wrote the rotated bit and atomically replaced the
    temp file. Then the metadata daemon having mmapped the old file detected
    the rotated bit and scheduled journal and tree file reopen+reread.
    
    However in concurrent environment like NFS homedir where multiple metadata
    daemons are handling the same database we may run in a race and not getting
    the rotated bit detected properly.
    
    This led to an infinite loop between meta_journal_add_entry() -
    meta_tree_flush_locked() - meta_tree_refresh_locked() - meta_journal_add_entry()
    since we had full journal, didn't detect the rotation and since the files
    were already unlinked, there was no force to break that loop. This patch
    forces tree file re-read after successful flush to prevent this issue.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=637095

 metadata/metatree.c |   14 ++++++++------
 1 files changed, 8 insertions(+), 6 deletions(-)
---
diff --git a/metadata/metatree.c b/metadata/metatree.c
index 3bcf9a6..015300e 100644
--- a/metadata/metatree.c
+++ b/metadata/metatree.c
@@ -169,7 +169,8 @@ struct _MetaTree {
   MetaJournal *journal;
 };
 
-static void         meta_tree_refresh_locked   (MetaTree    *tree);
+static void         meta_tree_refresh_locked   (MetaTree    *tree,
+                                               gboolean     force_reread);
 static MetaJournal *meta_journal_open          (MetaTree    *tree,
                                                const char  *filename,
                                                gboolean     for_write,
@@ -510,7 +511,7 @@ meta_tree_init (MetaTree *tree)
      journal. However we can detect this case by looking at the tree and see
      if its been rotated, we do this to ensure we have an uptodate tree+journal
      combo. */
-  meta_tree_refresh_locked (tree);
+  meta_tree_refresh_locked (tree, FALSE);
 
   return TRUE;
 
@@ -658,10 +659,10 @@ meta_tree_has_new_journal_entries (MetaTree *tree)
 
 /* Must be called with a write lock held */
 static void
-meta_tree_refresh_locked (MetaTree *tree)
+meta_tree_refresh_locked (MetaTree *tree, gboolean force_reread)
 {
   /* Needs to recheck since we dropped read lock */
-  if (meta_tree_needs_rereading (tree))
+  if (force_reread || meta_tree_needs_rereading (tree))
     {
       if (tree->header)
        meta_tree_clear (tree);
@@ -685,7 +686,7 @@ meta_tree_refresh (MetaTree *tree)
   if (needs_refresh)
     {
       g_rw_lock_writer_lock (&metatree_lock);
-      meta_tree_refresh_locked (tree);
+      meta_tree_refresh_locked (tree, FALSE);
       g_rw_lock_writer_unlock (&metatree_lock);
     }
 }
@@ -2363,7 +2364,8 @@ meta_tree_flush_locked (MetaTree *tree)
   res = meta_builder_write (builder,
                            meta_tree_get_filename (tree));
   if (res)
-    meta_tree_refresh_locked (tree);
+    /* Force re-read since we wrote a new file */
+    meta_tree_refresh_locked (tree, TRUE);
 
   meta_builder_free (builder);