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

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Message-ID: <20140318162319.GB5669@redhat.com>
Date:	Tue, 18 Mar 2014 17:23:19 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peng Tao <bergwolf@...il.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 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.

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.

> 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.

Oleg.

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