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 714201b01b78d9efbfaa110c9e27dfbb6e2a5557..7d3b83af3c3949049f84f95267df1eb48687e311 100644 (file)
--- 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 b9c89d899ea0d744246aa369d8417d8b5a1c4cec..d0a2c492fcebaf59b057a933aa691daa9e00c8af 100644 (file)
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -215,9 +215,9 @@ 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);
@@ -360,9 +360,9 @@ 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);
 
        /*
@@ -395,9 +395,9 @@ 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;