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From: Michal Hocko <mhocko@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	William Preston <wpreston@suse.com>,
	Roland McGrath <roland@hack.frob.com>,
	Andreas Schwab <schwab@suse.com>
Subject: Re: [RFC PATCH] kernel/fork: fix CLONE_CHILD_CLEARTID regression in nscd
Date: Fri, 19 Aug 2016 15:25:11 +0200	[thread overview]
Message-ID: <20160819132511.GH32619@dhcp22.suse.cz> (raw)
In-Reply-To: <20160812094113.GE3639@dhcp22.suse.cz>

On Fri 12-08-16 11:41:13, Michal Hocko wrote:
> On Wed 03-08-16 23:08:04, Oleg Nesterov wrote:
> > sorry for delay, I am travelling till the end of the week.
> 
> Same here...
> 
> > On 08/01, Michal Hocko wrote:
[...]
> > > We should also check for vfork because
> > > this is killable since d68b46fe16ad ("vfork: make it killable").
> > 
> > Hmm, why? Can't understand... In any case this check doesn't look right, the
> > comment says "a killed vfork parent" while tsk->vfork_done != NULL means it
> > is a vforked child.
> > 
> > So if we want this change, why we can't simply do
> > 
> > 	-	if (!(tsk->flags & PF_SIGNALED) &&
> > 	+	if (!(tsk->signal->flags & SIGNAL_GROUP_COREDUMP) &&
> > 
> > ?
> 
> This is what I had initially. But then the comment above the check made
> me worried that the parent of vforked child might get confused if the
> flag is cleared. I might have completely misunderstood the point of the
> comment though. So if you believe that vfork_done check is incorrect I
> can drop it. It shouldn't have any effect on the nscd usecase AFAIU.

So should I drop the vfork check and repost or we do not care about this
"regression" and declare nscd broken because it relies on a behavior
which is not in fact guaranteed by the kernel?
-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	William Preston <wpreston@suse.com>,
	Roland McGrath <roland@hack.frob.com>,
	Andreas Schwab <schwab@suse.com>
Subject: Re: [RFC PATCH] kernel/fork: fix CLONE_CHILD_CLEARTID regression in nscd
Date: Fri, 19 Aug 2016 15:25:11 +0200	[thread overview]
Message-ID: <20160819132511.GH32619@dhcp22.suse.cz> (raw)
In-Reply-To: <20160812094113.GE3639@dhcp22.suse.cz>

On Fri 12-08-16 11:41:13, Michal Hocko wrote:
> On Wed 03-08-16 23:08:04, Oleg Nesterov wrote:
> > sorry for delay, I am travelling till the end of the week.
> 
> Same here...
> 
> > On 08/01, Michal Hocko wrote:
[...]
> > > We should also check for vfork because
> > > this is killable since d68b46fe16ad ("vfork: make it killable").
> > 
> > Hmm, why? Can't understand... In any case this check doesn't look right, the
> > comment says "a killed vfork parent" while tsk->vfork_done != NULL means it
> > is a vforked child.
> > 
> > So if we want this change, why we can't simply do
> > 
> > 	-	if (!(tsk->flags & PF_SIGNALED) &&
> > 	+	if (!(tsk->signal->flags & SIGNAL_GROUP_COREDUMP) &&
> > 
> > ?
> 
> This is what I had initially. But then the comment above the check made
> me worried that the parent of vforked child might get confused if the
> flag is cleared. I might have completely misunderstood the point of the
> comment though. So if you believe that vfork_done check is incorrect I
> can drop it. It shouldn't have any effect on the nscd usecase AFAIU.

So should I drop the vfork check and repost or we do not care about this
"regression" and declare nscd broken because it relies on a behavior
which is not in fact guaranteed by the kernel?
-- 
Michal Hocko
SUSE Labs

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  reply	other threads:[~2016-08-19 13:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-01  8:14 [RFC PATCH] kernel/fork: fix CLONE_CHILD_CLEARTID regression in nscd Michal Hocko
2016-08-01  8:14 ` Michal Hocko
2016-08-03 21:08 ` Oleg Nesterov
2016-08-03 21:08   ` Oleg Nesterov
2016-08-12  9:41   ` Michal Hocko
2016-08-12  9:41     ` Michal Hocko
2016-08-19 13:25     ` Michal Hocko [this message]
2016-08-19 13:25       ` Michal Hocko
2016-08-23 15:27       ` Oleg Nesterov
2016-08-23 15:27         ` Oleg Nesterov
2016-08-23 16:03         ` Michal Hocko
2016-08-23 16:03           ` Michal Hocko

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