sort: avoid undefined operation with destroying locked mutex

This didn't seem to cause any invalid operation on GNU/Linux at least,
but depending on the implementation, mutex deadlocks could occur.
For example this might be the cause of lockups seen on Solaris:
http://lists.gnu.org/archive/html/coreutils/2013-03/msg00048.html

This was identified with valgrind 3.9.0 with this setup:

  seq 200000 > file.sort
  valgrind --tool=drd src/sort file.sort -o file.sort

With that, valgrind would _intermittently_ report the following:

 Destroying locked mutex: mutex 0x5419548, recursion count 1, owner 2.
    at 0x4C2E3F0: pthread_mutex_destroy(in vgpreload_drd-amd64-linux.so)
    by 0x409FA2: sortlines (sort.c:3649)
    by 0x409E26: sortlines (sort.c:3621)
    by 0x40AA9E: sort (sort.c:3955)
    by 0x40C5D9: main (sort.c:4739)
 mutex 0x5419548 was first observed at:
    at 0x4C2DE82: pthread_mutex_init(in vgpreload_drd-amd64-linux.so)
    by 0x409266: init_node (sort.c:3276)
    by 0x4092F4: init_node (sort.c:3286)
    by 0x4090DD: merge_tree_init (sort.c:3234)
    by 0x40AA5A: sort (sort.c:3951)
    by 0x40C5D9: main (sort.c:4739)

 Thread 2:
 The object at address 0x5419548 is not a mutex.
    at 0x4C2F4A4: pthread_mutex_unlock(in vgpreload_drd-amd64-linux.so)
    by 0x4093CA: unlock_node (sort.c:3323)
    by 0x409C85: merge_loop (sort.c:3531)
    by 0x409F8F: sortlines (sort.c:3644)
    by 0x409CE3: sortlines_thread (sort.c:3574)
    by 0x4E44F32: start_thread (in /usr/lib64/libpthread-2.18.so)
    by 0x514EEAC: clone (in /usr/lib64/libc-2.18.so)

* src/sort.c (sortlines): Move pthread_mutex_destroy() out to
merge_tree_destroy(), so that we don't overlap mutex destruction
with threads still operating on the nodes.
(sort): Call the destructors only with "lint" defined, as the
memory used will be deallocated implicitly at process end.
* NEWS: Mention the bug fix.

1 files changed, 15 insertions, 8 deletions

diff --git a/src/sort.c b/src/sort.c
index af95f7110..c24931920 100644
--- a/src/sort.c
+++ b/src/sort.c
@@ -3237,10 +3237,17 @@ merge_tree_init (size_t nthreads, size_t nlines, struct line *dest)
 
 /* Destroy the merge tree. */
 static void
-merge_tree_destroy (struct merge_node *merge_tree)
+merge_tree_destroy (size_t nthreads, struct merge_node *merge_tree)
 {
-  struct merge_node *root = merge_tree;
-  pthread_mutex_destroy (&root->lock);
+  size_t n_nodes = nthreads * 2;
+  struct merge_node *node = merge_tree;
+
+  while (n_nodes--)
+    {
+      pthread_mutex_destroy (&node->lock);
+      node++;
+    }
+
   free (merge_tree);
 }
 
@@ -3642,8 +3649,6 @@ sortlines (struct line *restrict lines, size_t nthreads,
       queue_insert (queue, node);
       merge_loop (queue, total_lines, tfp, temp_output);
     }
-
-  pthread_mutex_destroy (&node->lock);
 }
 
 /* Scan through FILES[NTEMPS .. NFILES-1] looking for files that are
@@ -3947,12 +3952,14 @@ sort (char *const *files, size_t nfiles, char const *output_file,
               queue_init (&queue, nthreads);
               struct merge_node *merge_tree =
                 merge_tree_init (nthreads, buf.nlines, line);
-              struct merge_node *root = merge_tree + 1;
 
-              sortlines (line, nthreads, buf.nlines, root,
+              sortlines (line, nthreads, buf.nlines, merge_tree + 1,
                          &queue, tfp, temp_output);
+
+#ifdef lint
+              merge_tree_destroy (nthreads, merge_tree);
               queue_destroy (&queue);
-              merge_tree_destroy (merge_tree);
+#endif
             }
           else
             write_unique (line - 1, tfp, temp_output);