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sigprocmask: Fix a signal-handler hang in case of a race condition.

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* lib/sigprocmask.c (overrides_handler_lock): Renamed from
overrides_lock.
(overrides_mt_lock): New variable.
(pthread_sigmask): Lock both locks.
(rpl_signal): Lock overrides_mt_lock, not overrides_lock.
This commit is contained in:
Bruno Haible
2026-04-10 22:57:04 +02:00
parent 91b5ffbdd9
commit a1a2837ec4
2 changed files with 24 additions and 10 deletions
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27
lib/sigprocmask.c
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@@ -223,8 +223,11 @@ struct override
static struct override overrides[NSIG] /* = { { 0, NULL }, ... } */;
/* A spin lock that protects overrides against simultaneous use from
different threads. */
static glwthread_spinlock_t overrides_lock = GLWTHREAD_SPIN_INIT;
different threads, outside signal handlers. */
static glwthread_spinlock_t overrides_mt_lock = GLWTHREAD_SPIN_INIT;
/* A spin lock that protects overrides against simultaneous use from
a signal handler and a pthread_sigmask invocation. */
static glwthread_spinlock_t overrides_handler_lock = GLWTHREAD_SPIN_INIT;
/* Signal handler that overrides an original one. */
static void
@@ -247,8 +250,8 @@ override_handler (int sig)
{
/* Another thread has already installed the override_handler but
is not yet done. Wait until it has finished the operation. */
glwthread_spin_lock (&overrides_lock);
glwthread_spin_unlock (&overrides_lock);
glwthread_spin_lock (&overrides_handler_lock);
glwthread_spin_unlock (&overrides_handler_lock);
/* Now overrides[sig].overridden must be true. */
if (!overrides[sig].overridden)
abort ();
@@ -300,7 +303,8 @@ pthread_sigmask (int operation, const sigset_t *set, sigset_t *old_set)
blocked_set |= 1U << sig;
if (!overrides[sig].overridden)
{
glwthread_spin_lock (&overrides_lock);
glwthread_spin_lock (&overrides_mt_lock);
glwthread_spin_lock (&overrides_handler_lock);
if (!overrides[sig].overridden)
{
/* Now it's OK to install the override_handler:
@@ -308,8 +312,10 @@ pthread_sigmask (int operation, const sigset_t *set, sigset_t *old_set)
condition since blocked_set already has the sig bit
set.
- If it gets invoked in another thread, the
overrides_lock protects it from proceeding until we
have stored the old_handler. */
overrides_handler_lock protects it from proceeding
until we have stored the old_handler. For this case,
it is important that the overrides_handler_lock is
the innermost taken lock. */
handler_t old_handler = signal (sig, override_handler);
if (old_handler != SIG_ERR)
{
@@ -323,7 +329,8 @@ pthread_sigmask (int operation, const sigset_t *set, sigset_t *old_set)
overrides[sig].overridden = 1;
}
}
glwthread_spin_unlock (&overrides_lock);
glwthread_spin_unlock (&overrides_handler_lock);
glwthread_spin_unlock (&overrides_mt_lock);
}
}
@@ -395,7 +402,7 @@ rpl_signal (int sig, handler_t handler)
{
/* Lock, in case of another thread calling pthread_sigmask, with the
effect of installing the override_handler (race condition). */
glwthread_spin_lock (&overrides_lock);
glwthread_spin_lock (&overrides_mt_lock);
if (overrides[sig].overridden)
{
result = overrides[sig].original_handler;
@@ -403,7 +410,7 @@ rpl_signal (int sig, handler_t handler)
}
else
result = signal (sig, handler);
glwthread_spin_unlock (&overrides_lock);
glwthread_spin_unlock (&overrides_mt_lock);
}
return result;
}