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dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=oleg@redhat.com Date: Thu, 29 Mar 2018 18:49:25 +0200 From: Oleg Nesterov To: Tejun Heo 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 Message-ID: <20180329164925.GA7175@redhat.com> References: <20180314194515.1661824-1-tj@kernel.org> <20180314194515.1661824-8-tj@kernel.org> <20180321155812.GA9382@redhat.com> <20180321164000.GC2149215@devbig577.frc2.facebook.com> <20180321171743.GA12834@redhat.com> <20180321175356.GD2149215@devbig577.frc2.facebook.com> <20180322112412.GA22183@redhat.com> <20180326150459.GE1840639@devbig577.frc2.facebook.com> <20180327142848.GA19341@redhat.com> <20180327155506.GA2779604@devbig577.frc2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327155506.GA2779604@devbig577.frc2.facebook.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 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.