Re: git: 69413598d266 - main - signal: use proc_iterate to save on work

On Mon, Sep 05, 2022 at 06:07:08PM +0200, Mateusz Guzik wrote:
> On 9/5/22, Konstantin Belousov <kostikbel@gmail.com> wrote:
> > On Mon, Sep 05, 2022 at 11:56:15AM +0000, Mateusz Guzik wrote:
> >> The branch main has been updated by mjg:
> >>
> >> URL:
> >> https://cgit.FreeBSD.org/src/commit/?id=69413598d2660054e29cac9454fe18c08e3bf36d
> >>
> >> commit 69413598d2660054e29cac9454fe18c08e3bf36d
> >> Author:     Mateusz Guzik <mjg@FreeBSD.org>
> >> AuthorDate: 2022-03-10 18:58:12 +0000
> >> Commit:     Mateusz Guzik <mjg@FreeBSD.org>
> >> CommitDate: 2022-09-05 11:54:47 +0000
> >>
> >>     signal: use proc_iterate to save on work
> >>
> >>     Most notably poudriere performs kill -9 -1 in jails for each port
> >>     being built. This reduces the scan from hundrends of processes to
> >>     literally 1.
> >>
> >>     Reviewed by:    jamie, markj
> >>     Differential Revision:  https://reviews.freebsd.org/D34522
> >> ---
> >>  sys/kern/kern_sig.c | 39 ++++++++++++++++++++++++++++-----------
> >>  1 file changed, 28 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
> >> index 6fd3eca0a14e..c50a37de07e6 100644
> >> --- a/sys/kern/kern_sig.c
> >> +++ b/sys/kern/kern_sig.c
> >> @@ -1776,18 +1776,13 @@ struct killpg1_ctx {
> >>  };
> >>
> >>  static void
> >> -killpg1_sendsig(struct proc *p, bool notself, struct killpg1_ctx *arg)
> >> +killpg1_sendsig_locked(struct proc *p, struct killpg1_ctx *arg)
> >>  {
> >>  	int err;
> >>
> >> -	if (p->p_pid <= 1 || (p->p_flag & P_SYSTEM) != 0 ||
> >> -	    (notself && p == arg->td->td_proc) || p->p_state == PRS_NEW)
> >> -		return;
> >> -	PROC_LOCK(p);
> >>  	err = p_cansignal(arg->td, p, arg->sig);
> >>  	if (err == 0 && arg->sig != 0)
> >>  		pksignal(p, arg->sig, arg->ksi);
> >> -	PROC_UNLOCK(p);
> >>  	if (err != ESRCH)
> >>  		arg->found = true;
> >>  	if (err == 0)
> >> @@ -1796,6 +1791,31 @@ killpg1_sendsig(struct proc *p, bool notself,
> >> struct killpg1_ctx *arg)
> >>  		arg->ret = err;
> >>  }
> >>
> >> +static void
> >> +killpg1_sendsig(struct proc *p, bool notself, struct killpg1_ctx *arg)
> >> +{
> >> +
> >> +	if (p->p_pid <= 1 || (p->p_flag & P_SYSTEM) != 0 ||
> >> +	    (notself && p == arg->td->td_proc) || p->p_state == PRS_NEW)
> >> +		return;
> >> +
> >> +	PROC_LOCK(p);
> >> +	killpg1_sendsig_locked(p, arg);
> >> +	PROC_UNLOCK(p);
> >> +}
> >> +
> >> +static void
> >> +kill_processes_prison_cb(struct proc *p, void *arg)
> >> +{
> >> +	struct killpg1_ctx *ctx = arg;
> >> +
> >> +	if (p->p_pid <= 1 || (p->p_flag & P_SYSTEM) != 0 ||
> >> +	    (p == ctx->td->td_proc) || p->p_state == PRS_NEW)
> > Extra ()
> >
> >> +		return;
> >> +
> >> +	killpg1_sendsig_locked(p, ctx);
> >> +}
> >> +
> >>  /*
> >>   * Common code for kill process group/broadcast kill.
> >>   * cp is calling process.
> >> @@ -1817,11 +1837,8 @@ killpg1(struct thread *td, int sig, int pgid, int
> >> all, ksiginfo_t *ksi)
> >>  		/*
> >>  		 * broadcast
> >>  		 */
> >> -		sx_slock(&allproc_lock);
> >> -		FOREACH_PROC_IN_SYSTEM(p) {
> >> -			killpg1_sendsig(p, true, &arg);
> >> -		}
> >> -		sx_sunlock(&allproc_lock);
> >> +		prison_proc_iterate(td->td_ucred->cr_prison,
> >> +		    kill_processes_prison_cb, &arg);
> >>  	} else {
> >>  		sx_slock(&proctree_lock);
> >>  		if (pgid == 0) {
> >
> > I believe before your change, kill(-1) would kill all processes in the
> > jail, which includes all processes in the nested jails.  Now, it seems
> > that linkage prevents iterating over the nested jails, am I missing it?
> >
> 
> See the pr_childcount check. If any jails pop up, there is a full scan
> like right now. And if the count transitions 0 -> 1 -> 0 during the
> iteration of the loop, there is nobody left to signal.
I see.

> 
> All previously existing races remain unaffected.
No, now you are potentially signalling some processes more than once.
Sending the signal is not idempotent operation.