r314708: panic: tdsendsignal: ksi on queue

[Konstantin Belousov]

On Fri, Mar 17, 2017 at 11:26:43AM -0700, Bryan Drewery wrote:
> On 3/10/2017 2:44 AM, Konstantin Belousov wrote:
> > On Fri, Mar 10, 2017 at 12:11:51AM +0100, Jilles Tjoelker wrote:
> >> This patch introduces a subtle correctness bug. A real SIGCHLD ksiginfo
> >> should always be the zombie's p_ksi; otherwise, the siginfo may be lost
> >> if there are too many signals pending for the target process or in the
> >> system. If the siginfo is lost and the reaper normally passes si_pid to
> >> waitpid() or similar (instead of passing WAIT_ANY or P_ALL), a zombie
> >> will remain until the reaper terminates.
> >>
> >> Conceptually the siginfo is sent to one process at a time only, so the
> >> bug is an artifact of the implementation. Perhaps the piece of code
> >> added in r309886 can be moved or the ksiginfo can be removed from the
> >> parent's queue.
> >>
> >> If such a fix is not possible, it may be better to send a bare SIGCHLD
> >> (si_code is SI_KERNEL or 0, depending on how many signals are pending)
> >> in this situation and document that reapers must use WAIT_ANY or P_ALL.
> >> (However, compared to the pre-r309886 situation they can still use
> >> SIGCHLD to get notified when to call waitpid() or similar.)
> >>
> > 
> > IMO it is acceptable for reaper to know and handle the case of lost
> > siginfo. But also it seems to be not too hard to guarantee the queueing
> > of the SIGCHLD for zombie re-parerning.
> > 
> > diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
> > index c524fe5df37..1a1dcc3a4c7 100644
> > --- a/sys/kern/kern_exit.c
> > +++ b/sys/kern/kern_exit.c
> > @@ -189,6 +189,7 @@ exit1(struct thread *td, int rval, int signo)
> >  {
> >  	struct proc *p, *nq, *q, *t;
> >  	struct thread *tdt;
> > +	ksiginfo_t *ksi, *ksi1;
> >  
> >  	mtx_assert(&Giant, MA_NOTOWNED);
> >  	KASSERT(rval == 0 || signo == 0, ("exit1 rv %d sig %d", rval, signo));
> > @@ -449,14 +450,23 @@ exit1(struct thread *td, int rval, int signo)
> >  		wakeup(q->p_reaper);
> >  	for (; q != NULL; q = nq) {
> >  		nq = LIST_NEXT(q, p_sibling);
> > +		ksi = ksiginfo_alloc(TRUE);
> >  		PROC_LOCK(q);
> >  		q->p_sigparent = SIGCHLD;
> >  
> >  		if (!(q->p_flag & P_TRACED)) {
> >  			proc_reparent(q, q->p_reaper);
> >  			if (q->p_state == PRS_ZOMBIE) {
> > +				if (q->p_ksi == NULL) {
> > +					ksi1 = NULL;
> > +				} else {
> > +					ksiginfo_copy(q->p_ksi, ksi);
> > +					ksi->ksi_flags |= KSI_INS;
> > +					ksi1 = ksi;
> > +					ksi = NULL;
> > +				}
> >  				PROC_LOCK(q->p_reaper);
> > -				pksignal(q->p_reaper, SIGCHLD, q->p_ksi);
> > +				pksignal(q->p_reaper, SIGCHLD, ksi1);
> >  				PROC_UNLOCK(q->p_reaper);
> >  			}
> >  		} else {
> > @@ -489,6 +499,8 @@ exit1(struct thread *td, int rval, int signo)
> >  			kern_psignal(q, SIGKILL);
> >  		}
> >  		PROC_UNLOCK(q);
> > +		if (ksi != NULL)
> > +			ksiginfo_free(ksi);
> >  	}
> >  
> >  	/*
> 
> 
> Ping?  Is this still progressing to be committed?
r315159 ?