Discourage use of pthread_atfork() for call_rcu handlers

[userspace-rcu.git] / README

diff --git a/README b/README
index e3800faad2d10cc5789c0a622c14f5ade9962ae1..97fba69462cc6e862578b942715316d40dfedecb 100644 (file)
--- a/README
+++ b/README
@@ -44,6 +44,21 @@ supported, with the following exceptions:
 - Alpha, ia64 and ARM architectures depend on 4.x gcc with atomic builtins
   support.
 
+For developers using the git tree:
+
+This source tree is based on the autotools suite from GNU to simplify
+portability. Here are some things you should have on your system in order to
+compile the git repository tree :
+
+- GNU autotools (automake >=1.10, autoconf >=2.50, autoheader >=2.50)
+  (make sure your system wide "automake" points to a recent version!)
+- GNU Libtool >=2.2
+  (for more information, go to http://www.gnu.org/software/autoconf/)
+
+If you get the tree from the repository, you will need to use the "bootstrap"
+script in the root of the tree. It calls all the GNU tools needed to prepare the
+tree configuration.
+
 
 QUICK START GUIDE
 -----------------
@@ -238,3 +253,17 @@ Interaction with fork()
        call_rcu_after_fork_parent() after the fork().  The child
        process must invoke call_rcu_after_fork_child().
        These three APIs are suitable for passing to pthread_atfork().
+       Even though these three APIs are suitable for passing to
+       pthread_atfork(), use of pthread_atfork() is *STRONGLY
+       DISCOURAGED* for programs calling the glibc memory allocator
+       (malloc(), calloc(), free(), ...) within call_rcu callbacks.
+       This is due to limitations in the way glibc memory allocator
+       handles calls to the memory allocator from concurrent threads
+       while the pthread_atfork() handlers are executing.
+       Combining e.g.:
+       * call to free() from callbacks executed within call_rcu worker
+         threads,
+       * executing call_rcu atfork handlers within the glibc pthread
+         atfork mechanism,
+       will sometimes trigger interesting process hangs. This usually
+       hangs on a memory allocator lock within glibc.