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From: Oleg Nesterov <oleg@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: torvalds@linux-foundation.org, jannh@google.com,
	paulmck@linux.vnet.ibm.com, bcrl@kvack.org,
	viro@zeniv.linux.org.uk, kent.overstreet@gmail.com,
	security@kernel.org, linux-kernel@vger.kernel.org,
	kernel-team@fb.com
Subject: Re: [PATCH 8/8] fs/aio: Use rcu_work instead of explicit rcu and work item
Date: Thu, 29 Mar 2018 18:49:25 +0200	[thread overview]
Message-ID: <20180329164925.GA7175@redhat.com> (raw)
In-Reply-To: <20180327155506.GA2779604@devbig577.frc2.facebook.com>

On 03/27, Tejun Heo wrote:
>
> On Tue, Mar 27, 2018 at 04:28:48PM +0200, Oleg Nesterov wrote:
> > > flush_*work() guarantees to wait for the completion of the latest
> > > instance of the work item which was visible to the caller.  We can't
> > > guarantee that w/o rcu_barrier().
> >
> > And this is what I can't understand.
> >
> > So let me repeat. Could you please describe a use-case which needs flush_rcuwork()
> > with rcu_barrier() ?
>
> So, if you skip that, flush_work() in itself won't wait for PENDING
> bit at all.  It'll return right away if the work item is waiting for
> rcu grace period.

Still no use-case... But yes, I forgot this is needed for correctness.

OK, thanks for your patience. But fyi now I hate this interface even more,
exactly because I was technically wrong in this discussion ;)

Oleg.

  reply	other threads:[~2018-03-29 16:49 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-14 19:41 [PATCHSET v2] percpu_ref, RCU: Audit RCU usages in percpu_ref users Tejun Heo
2018-03-14 19:45 ` [PATCH 1/8] fs/aio: Add explicit RCU grace period when freeing kioctx Tejun Heo
2018-03-14 19:45   ` [PATCH 2/8] fs/aio: Use RCU accessors for kioctx_table->table[] Tejun Heo
2018-03-14 19:45   ` [PATCH 3/8] RDMAVT: Fix synchronization around percpu_ref Tejun Heo
2018-03-15 22:24     ` Jason Gunthorpe
2018-03-14 19:45   ` [PATCH 4/8] HMM: Remove superflous RCU protection around radix tree lookup Tejun Heo
2018-03-14 19:45     ` Tejun Heo
2018-03-26 14:54     ` Tejun Heo
2018-03-26 14:54       ` Tejun Heo
2018-03-27 16:12       ` Jerome Glisse
2018-03-27 16:12         ` Jerome Glisse
2018-03-14 19:45   ` [PATCH 5/8] percpu_ref: Update doc to dissuade users from depending on internal RCU grace periods Tejun Heo
2018-03-19 17:10     ` Tejun Heo
2018-03-14 19:45   ` [PATCH 6/8] RCU, workqueue: Implement rcu_work Tejun Heo
2018-03-14 20:13     ` Paul E. McKenney
2018-03-16  6:01     ` Lai Jiangshan
2018-03-19 16:45       ` Tejun Heo
2018-03-20 10:04         ` Lai Jiangshan
2018-03-14 19:45   ` [PATCH 7/8] cgroup: Use rcu_work instead of explicit rcu and work item Tejun Heo
2018-03-14 19:45   ` [PATCH 8/8] fs/aio: " Tejun Heo
2018-03-19 17:12     ` Tejun Heo
2018-03-21 15:58     ` Oleg Nesterov
2018-03-21 16:40       ` Tejun Heo
2018-03-21 17:17         ` Oleg Nesterov
2018-03-21 17:53           ` Tejun Heo
2018-03-22 11:24             ` Oleg Nesterov
2018-03-26 15:04               ` Tejun Heo
2018-03-27 14:28                 ` Oleg Nesterov
2018-03-27 15:55                   ` Tejun Heo
2018-03-29 16:49                     ` Oleg Nesterov [this message]
2018-03-29 17:41                       ` Tejun Heo

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