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spf=pass smtp.mailfrom=htejun@gmail.com X-Google-Smtp-Source: AG47ELteHEojmpCJE41WMQ0qviOrD295svsBm6mqs/L9Bys9sZIuB8wa3NA4uGjSZwHx+ICLuLU2pg== Sender: Tejun Heo Date: Tue, 27 Mar 2018 08:55:06 -0700 From: Tejun Heo To: Oleg Nesterov 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: <20180327155506.GA2779604@devbig577.frc2.facebook.com> References: <20180314194205.1651587-1-tj@kernel.org> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327142848.GA19341@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Hey, 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. Thanks. -- tejun