On Thu, Nov 11, 2021 at 08:53:20PM +0100, Mark Kettenis wrote:
> > Date: Thu, 11 Nov 2021 13:30:04 -0600
> > From: Scott Cheloha <scottchel...@gmail.com>
> >
> > My understanding of sigsuspend(2) is that it only returns if a signal
> > is delivered to the calling thread. However, in sys_sigsuspend() we
> > pass &p->p_p->ps_sigacts as the wakeup channel to tsleep_nsec(9).
> >
> > Are we actually waiting for a wakeup on that channel? Or can we sleep
> > on &nowake here? Patch attached. Note that we don't need to loop
> > here anymore: we can't receieve wakeup so tsleep_nsec(9) will never
> > return zero.
>
> I don't think we expect a wakeup on that channel. But the loop is
> still needed as a spurious wakeup may happen.
I'm not quite sure how you'd get a spurious wakeup in this context,
but I'll take your word for it.
So use &nowake to indicate we're not expecting a wakeup, but keep the
loop.
Index: kern_sig.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_sig.c,v
retrieving revision 1.287
diff -u -p -r1.287 kern_sig.c
--- kern_sig.c 24 Oct 2021 00:02:25 -0000 1.287
+++ kern_sig.c 11 Nov 2021 20:10:51 -0000
@@ -509,7 +509,7 @@ dosigsuspend(struct proc *p, sigset_t ne
}
/*
- * Suspend process until signal, providing mask to be set
+ * Suspend thread until signal, providing mask to be set
* in the meantime. Note nonstandard calling convention:
* libc stub passes mask, not pointer, to save a copyin.
*/
@@ -519,12 +519,10 @@ sys_sigsuspend(struct proc *p, void *v,
struct sys_sigsuspend_args /* {
syscallarg(int) mask;
} */ *uap = v;
- struct process *pr = p->p_p;
- struct sigacts *ps = pr->ps_sigacts;
dosigsuspend(p, SCARG(uap, mask) &~ sigcantmask);
- while (tsleep_nsec(ps, PPAUSE|PCATCH, "sigsusp", INFSLP) == 0)
- /* void */;
+ while (tsleep_nsec(&nowake, PPAUSE|PCATCH, "sigsusp", INFSLP) == 0)
+ continue;
/* always return EINTR rather than ERESTART... */
return (EINTR);
}
