> Date: Tue, 14 Jan 2020 10:34:05 +1100
> From: Jonathan Gray <j...@jsg.id.au>
>
> On Mon, Jan 13, 2020 at 05:02:12PM +0100, Martin Pieuchot wrote:
> > I'm facing a lock ordering issue while profiling the scheduler which
> > cannot be solved without using a different lock for the global sleepqueue
> > and the runqueues.
> >
> > The SCHED_LOCK() currently protects both data structures as well as the
> > related fields in 'struct proc'. One of this fields is `p_wchan' which
> > is obviously related to the global sleepqueue.
> >
> > The cleaning diff below introduces a new function, awake(), that unify
> > the multiple uses of the following idiom:
> >
> > if (p->p_stat == SSLEEP)
> > setrunnable(p);
> > else
> > unsleep(p);
> >
> > This is generally done after checking if the thread `p' is on the
> > sleepqueue.
>
> Why not name it wakeup_proc() instead or something like endsleep()?
>
> awake() does not describe the action that is being done and
> if (awake()) reads like it could be
> if (p->p_stat != SSLEEP && p->p_stat != SSTOP)
Must say I had reservations about the "awake" name as well, but jsg@
nails it here since it both a verb and an adjective which creates
confusion. Both names suggester here are find I think.
> > This diff introduces a change in behavior in the Linux compat:
> > wake_up_process() will now return 1 if the thread was stopped and not
> > sleeping. This should be fine since the only place this value is
> > checked is with the combination of task_asleep().
> >
> > While here I removed two unnecessary `p_wchan' check before unsleep().
> >
> > ok?
> >
> > Index: dev/pci/drm/drm_linux.c
> > ===================================================================
> > RCS file: /cvs/src/sys/dev/pci/drm/drm_linux.c,v
> > retrieving revision 1.55
> > diff -u -p -r1.55 drm_linux.c
> > --- dev/pci/drm/drm_linux.c 5 Jan 2020 13:46:02 -0000 1.55
> > +++ dev/pci/drm/drm_linux.c 13 Jan 2020 15:34:44 -0000
> > @@ -115,20 +115,8 @@ schedule_timeout(long timeout)
> > int
> > wake_up_process(struct proc *p)
> > {
> > - int s, r = 0;
> > -
> > - SCHED_LOCK(s);
> > atomic_cas_ptr(&sch_proc, p, NULL);
> > - if (p->p_wchan) {
> > - if (p->p_stat == SSLEEP) {
> > - setrunnable(p);
> > - r = 1;
> > - } else
> > - unsleep(p);
> > - }
> > - SCHED_UNLOCK(s);
> > -
> > - return r;
> > + return awake(p, NULL);
> > }
> >
> > void
> > Index: kern/sys_generic.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/sys_generic.c,v
> > retrieving revision 1.127
> > diff -u -p -r1.127 sys_generic.c
> > --- kern/sys_generic.c 8 Jan 2020 16:27:41 -0000 1.127
> > +++ kern/sys_generic.c 13 Jan 2020 15:35:22 -0000
> > @@ -767,7 +767,6 @@ void
> > selwakeup(struct selinfo *sip)
> > {
> > struct proc *p;
> > - int s;
> >
> > KNOTE(&sip->si_note, NOTE_SUBMIT);
> > if (sip->si_seltid == 0)
> > @@ -780,15 +779,10 @@ selwakeup(struct selinfo *sip)
> > p = tfind(sip->si_seltid);
> > sip->si_seltid = 0;
> > if (p != NULL) {
> > - SCHED_LOCK(s);
> > - if (p->p_wchan == (caddr_t)&selwait) {
> > - if (p->p_stat == SSLEEP)
> > - setrunnable(p);
> > - else
> > - unsleep(p);
> > + if (awake(p, &selwait)) {
> > + /* nothing else to do */
> > } else if (p->p_flag & P_SELECT)
> > atomic_clearbits_int(&p->p_flag, P_SELECT);
> > - SCHED_UNLOCK(s);
> > }
> > }
> >
> > Index: kern/kern_synch.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/kern_synch.c,v
> > retrieving revision 1.156
> > diff -u -p -r1.156 kern_synch.c
> > --- kern/kern_synch.c 12 Jan 2020 00:01:12 -0000 1.156
> > +++ kern/kern_synch.c 13 Jan 2020 15:41:00 -0000
> > @@ -469,8 +469,7 @@ sleep_setup_signal(struct sleep_state *s
> > */
> > atomic_setbits_int(&p->p_flag, P_SINTR);
> > if (p->p_p->ps_single != NULL || (sls->sls_sig = CURSIG(p)) != 0) {
> > - if (p->p_wchan)
> > - unsleep(p);
> > + unsleep(p);
> > p->p_stat = SONPROC;
> > sls->sls_do_sleep = 0;
> > } else if (p->p_wchan == 0) {
> > @@ -505,6 +504,25 @@ sleep_finish_signal(struct sleep_state *
> > return (error);
> > }
> >
> > +int
> > +awake(struct proc *p, const volatile void *chan)
> > +{
> > + int s, awakened = 0;
> > +
> > + SCHED_LOCK(s);
> > + if (p->p_wchan != NULL &&
> > + ((chan == NULL) || (p->p_wchan == chan))) {
> > + awakened = 1;
> > + if (p->p_stat == SSLEEP)
> > + setrunnable(p);
> > + else
> > + unsleep(p);
> > + }
> > + SCHED_UNLOCK(s);
> > +
> > + return awakened;
> > +}
> > +
> > /*
> > * Implement timeout for tsleep.
> > * If process hasn't been awakened (wchan non-zero),
> > @@ -515,17 +533,9 @@ void
> > endtsleep(void *arg)
> > {
> > struct proc *p = arg;
> > - int s;
> >
> > - SCHED_LOCK(s);
> > - if (p->p_wchan) {
> > - if (p->p_stat == SSLEEP)
> > - setrunnable(p);
> > - else
> > - unsleep(p);
> > + if (awake(p, NULL))
> > atomic_setbits_int(&p->p_flag, P_TIMEOUT);
> > - }
> > - SCHED_UNLOCK(s);
> > }
> >
> > /*
> > @@ -536,7 +546,7 @@ unsleep(struct proc *p)
> > {
> > SCHED_ASSERT_LOCKED();
> >
> > - if (p->p_wchan) {
> > + if (p->p_wchan != NULL) {
> > TAILQ_REMOVE(&slpque[LOOKUP(p->p_wchan)], p, p_runq);
> > p->p_wchan = NULL;
> > }
> > @@ -570,13 +580,8 @@ wakeup_n(const volatile void *ident, int
> > if (p->p_stat != SSLEEP && p->p_stat != SSTOP)
> > panic("wakeup: p_stat is %d", (int)p->p_stat);
> > #endif
> > - if (p->p_wchan == ident) {
> > + if (awake(p, ident))
> > --n;
> > - p->p_wchan = 0;
> > - TAILQ_REMOVE(qp, p, p_runq);
> > - if (p->p_stat == SSLEEP)
> > - setrunnable(p);
> > - }
> > }
> > SCHED_UNLOCK(s);
> > }
> > Index: kern/vfs_sync.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/vfs_sync.c,v
> > retrieving revision 1.61
> > diff -u -p -r1.61 vfs_sync.c
> > --- kern/vfs_sync.c 8 Dec 2019 12:29:42 -0000 1.61
> > +++ kern/vfs_sync.c 13 Jan 2020 15:25:02 -0000
> > @@ -241,12 +241,8 @@ syncer_thread(void *arg)
> > int
> > speedup_syncer(void)
> > {
> > - int s;
> > -
> > - SCHED_LOCK(s);
> > - if (syncerproc && syncerproc->p_wchan == &lbolt)
> > - setrunnable(syncerproc);
> > - SCHED_UNLOCK(s);
> > + if (syncerproc)
> > + awake(syncerproc, &lbolt);
> > if (rushjob < syncdelay / 2) {
> > rushjob += 1;
> > stat_rush_requests += 1;
> > Index: sys/proc.h
> > ===================================================================
> > RCS file: /cvs/src/sys/sys/proc.h,v
> > retrieving revision 1.284
> > diff -u -p -r1.284 proc.h
> > --- sys/proc.h 6 Jan 2020 10:25:10 -0000 1.284
> > +++ sys/proc.h 13 Jan 2020 15:35:52 -0000
> > @@ -564,6 +564,7 @@ void procinit(void);
> > void setpriority(struct proc *, uint32_t, uint8_t);
> > void setrunnable(struct proc *);
> > void endtsleep(void *);
> > +int awake(struct proc *, const volatile void *);
> > void unsleep(struct proc *);
> > void reaper(void *);
> > void exit1(struct proc *, int, int, int);
> > Index: kern/kern_sig.c
> > ===================================================================
> > RCS file: /cvs/src/sys/kern/kern_sig.c,v
> > retrieving revision 1.240
> > diff -u -p -r1.240 kern_sig.c
> > --- kern/kern_sig.c 8 Jan 2020 16:27:41 -0000 1.240
> > +++ kern/kern_sig.c 13 Jan 2020 15:36:37 -0000
> > @@ -1109,7 +1109,7 @@ ptsignal(struct proc *p, int signum, enu
> > * runnable and can look at the signal. But don't make
> > * the process runnable, leave it stopped.
> > */
> > - if (p->p_wchan && p->p_flag & P_SINTR)
> > + if (p->p_flag & P_SINTR)
> > unsleep(p);
> > goto out;
> >
> >
> >
>
>
