From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <jiangshanlai+lkml@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Jann Horn <jannh@google.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Benjamin LaHaise <bcrl@kvack.org>,
Al Viro <viro@zeniv.linux.org.uk>,
Kent Overstreet <kent.overstreet@gmail.com>,
security@kernel.org, LKML <linux-kernel@vger.kernel.org>,
kernel-team@fb.com
Subject: Re: [PATCH 6/8] RCU, workqueue: Implement rcu_work
Date: Mon, 19 Mar 2018 09:45:23 -0700 [thread overview]
Message-ID: <20180319164523.GB519464@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <CAJhGHyA3zte-0MWGC+DrOptprHBRroCn8fHM678iVnb-1VStLA@mail.gmail.com>
Hello, Lai.
On Fri, Mar 16, 2018 at 02:01:35PM +0800, Lai Jiangshan wrote:
> > +bool flush_rcu_work(struct rcu_work *rwork)
> > +{
> > + if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
> > + rcu_barrier();
> > + flush_work(&rwork->work);
> > + return true;
>
> A possible tiny improvement: check if it was already queued on wq.
> For example:
>
> if (test_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&rwork->work))) {
> if (!flush_work(&rwork->work)) {
> rcu_barrier();
> flush_work(&rwork->work);
> }
> return true;
But this breaks the guarantee that flush_work waits for the latest
queueing instance. Please consider the following scenario.
1. rcu-work is queued
2. rcu-work starts executing
3. rcu-work is queued again
4. rcu-work is flushed
5. execution finishes
6. flush finishes
7. execution finishes
6 should happen after 7 but it didn't.
Thanks.
--
tejun
next prev parent reply other threads:[~2018-03-19 16:45 UTC|newest]
Thread overview: 28+ 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
2018-03-26 14:54 ` Tejun Heo
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 [this message]
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
2018-03-29 17:41 ` Tejun Heo
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