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

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.

All previously existing races remain unaffected.

-- 
Mateusz Guzik <mjguzik gmail.com>