From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Fri, 10 May 2013 11:30:18 +0000 (-0400)
Subject: Fix: Use a filled signal mask to disable all signals
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=f425e7ad9f0f7d291dfa08fce0215eb2ed94e416;p=userspace-rcu.git

Fix: Use a filled signal mask to disable all signals

Changelog from David Pelton's original patch:

While using lttng-ust with an application that was calling fork()
with pending signals, I found that all signals were getting unmasked
shortly before the underlying call to fork().  After some
investigation, I found that the rcu_bp_before_fork() function was
unmasking all signals.  Based on the comments for this function, it
should be masking all signals.  Inspection of the rest of the code
in urcu-bp.c revealed the same pattern in two other functions.

This patch changes the code to use a filled signal mask to disable
all signals.  The change to rcu_bp_before_fork() addressed the
problem I was seeing while using lttng-ust.  The changes to the
other two functions appear to fix other instances of the same
problem.

Updates by Mathieu Desnoyers:

- Use SIG_BLOCK instead of SIG_SETMASK when setting a filled mask. This
  has the same behavior in this case (since we're blocking all signals),
  but is semantically neater: if we ever some signals from that mask,
  we'd like to to a union with the signal mask already blocked by the
  application.
- Also fix incorrect signal masking in compat_arch_x86.c.

Reported-by: David Pelton <dpelton@ciena.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/compat_arch_x86.c b/compat_arch_x86.c
index 714201b..7d3b83a 100644
--- a/compat_arch_x86.c
+++ b/compat_arch_x86.c
@@ -80,9 +80,9 @@ static void mutex_lock_signal_save(pthread_mutex_t *mutex, sigset_t *oldmask)
 	int ret;
 
 	/* Disable signals */
-	ret = sigemptyset(&newmask);
+	ret = sigfillset(&newmask);
 	assert(!ret);
-	ret = pthread_sigmask(SIG_SETMASK, &newmask, oldmask);
+	ret = pthread_sigmask(SIG_BLOCK, &newmask, oldmask);
 	assert(!ret);
 	ret = pthread_mutex_lock(&compat_mutex);
 	assert(!ret);
diff --git a/urcu-bp.c b/urcu-bp.c
index f3249b4..603cdf0 100644
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -210,9 +210,9 @@ void synchronize_rcu(void)
 	sigset_t newmask, oldmask;
 	int ret;
 
-	ret = sigemptyset(&newmask);
+	ret = sigfillset(&newmask);
 	assert(!ret);
-	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
+	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 	assert(!ret);
 
 	mutex_lock(&rcu_gp_lock);
@@ -355,9 +355,9 @@ void rcu_bp_register(void)
 	sigset_t newmask, oldmask;
 	int ret;
 
-	ret = sigemptyset(&newmask);
+	ret = sigfillset(&newmask);
 	assert(!ret);
-	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
+	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 	assert(!ret);
 
 	/*
@@ -390,9 +390,9 @@ void rcu_bp_before_fork(void)
 	sigset_t newmask, oldmask;
 	int ret;
 
-	ret = sigemptyset(&newmask);
+	ret = sigfillset(&newmask);
 	assert(!ret);
-	ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
+	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 	assert(!ret);
 	mutex_lock(&rcu_gp_lock);
 	saved_fork_signal_mask = oldmask;