linux-kernel - Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive

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Date:	Wed, 19 Mar 2014 10:22:59 +0800
From:	Peng Tao <bergwolf@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Oleg Drokin <oleg.drokin@...el.com>,
	Andreas Dilger <andreas.dilger@...el.com>
Subject: Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive_head

On Wed, Mar 19, 2014 at 12:23 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 03/18, Peng Tao wrote:
>>
>> On Tue, Mar 18, 2014 at 10:05 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> >
>> > Unless you cannot use ___wait() and really need to open-code the
>> > wait_event() stuff.
>> >
>> Lustre's private l_wait_event() stuff takes care to (un)mask
>> LUSTRE_FATAL_SIGS
>
> Hmm. This is off-topic but after the quick grep LUSTRE_FATAL_SIGS/etc
> looks suspicious.
>
> Firtsly, cfs_block_sigs/cfs_block_sigsinv/etc are not exactly right,
> they need set_current_blocked(). And you can read "old" lockless.
>
It seems that set_current_blocked() is not exported. Can we ask to export it?

And looking at other similar places like coda_block_signals(), it
doesn't call set_current_blocked() either. So it needs
set_current_blocked() as well.

> And note that cfs_block_sigsinv(0) (which should block all signals)
> can't actually protect from SIGKILL (or in fact from another fatal
> signal) or SIGSTOP if the caller is multithreaded. Or ptrace, or
> freezer.
>
>> and always wait in TASK_INTERRUPTIBLE state.
>
> and it seems that __wstate passed to waitq_wait/waitq_timedwait is
> simply ignored.
>
Yes. That needs to be dropped.

>> It looks to me that we can at least wrap l_wait_event() on top of
>> wait_event_interruptible/wait_event_timeout_interruptible.
>
> l_wait_event looks really complicated ;) but perhaps you can rewrite
> it on top of ___wait_event(), note that condition/cmd can do anything
> you want.
>
Yeah, I meant to say __wait_event(). Thanks for correcting me.

Thanks,
Tao
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