From 8d107d12102747d3d8691aea11c17e37f43fb70d Mon Sep 17 00:00:00 2001
From: Jason Evans <jasone@FreeBSD.org>
Date: Tue, 27 Jun 2000 21:30:16 +0000
Subject: If multiple threads are blocked in sigwait() for the same signal that
 does not have a user-supplied signal handler, when a signal is delivered, one
 thread will receive the signal, and then the code reverts to having no signal
 handler for the signal.  This can leave the other sigwait()ing threads
 stranded permanently if the signal is later ignored, or can result in process
 termination when the process should have delivered the signal to one of the
 threads in sigwait().

To fix this problem, maintain a count of sigwait()ers for each signal that
has no default signal handler.  Use the count to correctly install/uninstall
dummy signal handlers.

Reviewed by:	deischen
---
 lib/libpthread/thread/thr_init.c    |  3 +++
 lib/libpthread/thread/thr_private.h |  7 +++++++
 lib/libpthread/thread/thr_sigwait.c | 31 +++++++++++++++++++++++++++----
 3 files changed, 37 insertions(+), 4 deletions(-)

(limited to 'lib/libpthread/thread')

diff --git a/lib/libpthread/thread/thr_init.c b/lib/libpthread/thread/thr_init.c
index dd5f53fac64e..8e13f90dc993 100644
--- a/lib/libpthread/thread/thr_init.c
+++ b/lib/libpthread/thread/thr_init.c
@@ -277,6 +277,9 @@ _thread_init(void)
 				 */
 				PANIC("Cannot read signal handler info");
 			}
+
+			/* Initialize the SIG_DFL dummy handler count. */
+			_thread_dfl_count[i] = 0;
 		}
 
 		/*
diff --git a/lib/libpthread/thread/thr_private.h b/lib/libpthread/thread/thr_private.h
index 6b48f2389b6e..1ecda3c2e211 100644
--- a/lib/libpthread/thread/thr_private.h
+++ b/lib/libpthread/thread/thr_private.h
@@ -929,6 +929,13 @@ SCLASS	pthread_cond_t  _gc_cond
  */
 SCLASS struct  sigaction _thread_sigact[NSIG];
 
+/*
+ * Array of counts of dummy handlers for SIG_DFL signals.  This is used to
+ * assure that there is always a dummy signal handler installed while there is a
+ * thread sigwait()ing on the corresponding signal.
+ */
+SCLASS int	_thread_dfl_count[NSIG];
+
 /*
  * Pending signals for this process.
  */
diff --git a/lib/libpthread/thread/thr_sigwait.c b/lib/libpthread/thread/thr_sigwait.c
index a50968768082..b12c028740c9 100644
--- a/lib/libpthread/thread/thr_sigwait.c
+++ b/lib/libpthread/thread/thr_sigwait.c
@@ -94,6 +94,12 @@ sigwait(const sigset_t * set, int *sig)
 		return (0);
 	}
 
+	/*
+	 * Access the _thread_dfl_count array under the protection of signal
+	 * deferral.
+	 */
+	_thread_kern_sig_defer();
+
 	/*
 	 * Enter a loop to find the signals that are SIG_DFL.  For
 	 * these signals we must install a dummy signal handler in
@@ -107,10 +113,16 @@ sigwait(const sigset_t * set, int *sig)
 	for (i = 1; i < NSIG; i++) {
 		if (sigismember(&waitset, i) &&
 		    (_thread_sigact[i - 1].sa_handler == SIG_DFL)) {
-			if (_thread_sys_sigaction(i,&act,NULL) != 0)
-				ret = -1;
+			_thread_dfl_count[i]++;
+			if (_thread_dfl_count[i] == 1) {
+				if (_thread_sys_sigaction(i,&act,NULL) != 0)
+					ret = -1;
+			}
 		}
 	}
+	/* Done accessing _thread_dfl_count for now. */
+	_thread_kern_sig_undefer();
+
 	if (ret == 0) {
 		/*
 		 * Save the wait signal mask.  The wait signal
@@ -132,15 +144,26 @@ sigwait(const sigset_t * set, int *sig)
 		_thread_run->data.sigwait = NULL;
 	}
 
+	/*
+	 * Access the _thread_dfl_count array under the protection of signal
+	 * deferral.
+	 */
+	_thread_kern_sig_defer();
+
 	/* Restore the sigactions: */
 	act.sa_handler = SIG_DFL;
 	for (i = 1; i < NSIG; i++) {
 		if (sigismember(&waitset, i) &&
 		    (_thread_sigact[i - 1].sa_handler == SIG_DFL)) {
-			if (_thread_sys_sigaction(i,&act,NULL) != 0)
-				ret = -1;
+			_thread_dfl_count[i]--;
+			if (_thread_dfl_count == 0) {
+				if (_thread_sys_sigaction(i,&act,NULL) != 0)
+					ret = -1;
+			}
 		}
 	}
+	/* Done accessing _thread_dfl_count. */
+	_thread_kern_sig_undefer();
 
 	_thread_leave_cancellation_point();
 	
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