Fix a long standing race between sleep queue and thread

suspension code. When a thread A is going to sleep, it calls
sleepq_catch_signals() to detect any pending signals or thread
suspension request, if nothing happens, it returns without
holding process lock or scheduler lock, this opens a race
window which allows thread B to come in and do process
suspension work, however since A is still at running state,
thread B can do nothing to A, thread A continues, and puts
itself into actually sleeping state, but B has never seen it,
and it sits there forever until B is woken up by other threads
sometimes later(this can be very long delay or never
happen). Fix this bug by forcing sleepq_catch_signals to
return with scheduler lock held.
Fix sleepq_abort() by passing it an interrupted code, previously,
it worked as wakeup_one(), and the interruption can not be
identified correctly by sleep queue code when the sleeping
thread is resumed.
Let thread_suspend_check() returns EINTR or ERESTART, so sleep
queue no longer has to use SIGSTOP as a hack to build a return
value.

Reviewed by:	jhb
MFC after:	1 week

1 files changed, 2 insertions, 9 deletions

diff --git a/sys/kern/kern_condvar.c b/sys/kern/kern_condvar.c
index ede6b61..f430ea8 100644
--- a/sys/kern/kern_condvar.c
+++ b/sys/kern/kern_condvar.c
@@ -166,7 +166,7 @@ cv_wait_sig(struct cv *cvp, struct mtx *mp)
 {
 	struct thread *td;
 	struct proc *p;
-	int rval, sig;
+	int rval;
 	WITNESS_SAVE_DECL(mp);
 
 	td = curthread;
@@ -210,10 +210,7 @@ cv_wait_sig(struct cv *cvp, struct mtx *mp)
 
 	sleepq_add(cvp, mp, cvp->cv_description, SLEEPQ_CONDVAR |
 	    SLEEPQ_INTERRUPTIBLE);
-	sig = sleepq_catch_signals(cvp);
 	rval = sleepq_wait_sig(cvp);
-	if (rval == 0)
-		rval = sleepq_calc_signal_retval(sig);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))
@@ -292,7 +289,6 @@ cv_timedwait_sig(struct cv *cvp, struct mtx *mp, int timo)
 	struct thread *td;
 	struct proc *p;
 	int rval;
-	int sig;
 	WITNESS_SAVE_DECL(mp);
 
 	td = curthread;
@@ -338,10 +334,7 @@ cv_timedwait_sig(struct cv *cvp, struct mtx *mp, int timo)
 	sleepq_add(cvp, mp, cvp->cv_description, SLEEPQ_CONDVAR |
 	    SLEEPQ_INTERRUPTIBLE);
 	sleepq_set_timeout(cvp, timo);
-	sig = sleepq_catch_signals(cvp);
-	rval = sleepq_timedwait_sig(cvp, sig != 0);
-	if (rval == 0)
-		rval = sleepq_calc_signal_retval(sig);
+	rval = sleepq_timedwait_sig(cvp);
 
 #ifdef KTRACE
 	if (KTRPOINT(td, KTR_CSW))