X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=README;h=d7dde388b453efe8bdf71fe2d015b9ef73466abd;hb=378ea6a26277f6db3c195b2126c5f4d35d270174;hp=303c6ec48fc0fd948de29d1bc1319e523d7eadd4;hpb=88ecbe6daa6da4850ea975b635cd1af8e4ca9bfe;p=urcu.git

diff --git a/README b/README
index 303c6ec..d7dde38 100644
--- a/README
+++ b/README
@@ -259,4 +259,24 @@ Interaction with fork()
 	must invoke call_rcu_before_fork() before the fork() and
 	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.
+
+Thread Local Storage (TLS)
+
+	Userspace RCU can fall back on pthread_getspecific() to emulate
+	TLS variables on systems where it is not available. This behavior
+	can be forced by specifying --disable-compiler-tls as configure
+	argument.