From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Tue, 26 Jul 2016 20:54:55 +0000 (-0400)
Subject: Fix: pre-fault TLS in ust-malloc instrumentation
X-Git-Tag: v2.9.0-rc1~27
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=f4a90c3e8f3f5e8dd5c1896afb82fa96c1a32f22;p=lttng-ust.git

Fix: pre-fault TLS in ust-malloc instrumentation

Faulting the TLS variable when accessed for the first time can trigger
deadlocks with internal libc lock when using the liblttng-ust-malloc
wrapper. Fix this by pre-faulting it in a library constructor, similarly
to the approach taken for all other TLS variables in lttng-ust.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/liblttng-ust-libc-wrapper/lttng-ust-malloc.c b/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
index 5d290445..f3e1e19e 100644
--- a/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
+++ b/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
@@ -421,6 +421,12 @@ int posix_memalign(void **memptr, size_t alignment, size_t size)
 	return retval;
 }
 
+static
+void lttng_ust_fixup_malloc_nesting_tls(void)
+{
+	asm volatile ("" : : "m" (URCU_TLS(malloc_nesting)));
+}
+
 __attribute__((constructor))
 void lttng_ust_malloc_wrapper_init(void)
 {
@@ -428,6 +434,7 @@ void lttng_ust_malloc_wrapper_init(void)
 	if (cur_alloc.calloc) {
 		return;
 	}
+	lttng_ust_fixup_malloc_nesting_tls();
 	/*
 	 * Ensure the allocator is in place before the process becomes
 	 * multithreaded.