sort: avoid segfault when using two or more threads

This change does not fix the actual bug.  That was done by commit
c9db0ac6, "sort: preallocate merge tree nodes to heap".  The fix
was to store each "node" structure on the heap, not on the stack.
Otherwise, a node from one thread's stack could be used in another
thread after the first thread had expired (via pthread_join).
This bug was very hard to trigger when using spinlocks, but
easier once we began using mutexes.
* NEWS (Bug fixes): Mention it.
For details, see http://debbugs.gnu.org/7597.

diff --git a/NEWS b/NEWS
index 9f55cbb..b0a11b1 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,9 @@ GNU coreutils NEWS                                    -*- outline -*-
   do no work.  I.e., "sort < big-file | less" could waste a lot of power.
   [bug introduced in coreutils-8.6]
 
+  sort with at least two threads no longer segfaults due to use of pointers
+  into the stack of an expired thread. [bug introduced in coreutils-8.6]
+
 ** New features
 
   split accepts the --number option to generate a specific number of files.