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x-google-dkim=pass (2048-bit rsa key) header.d=1e100.net header.i=@1e100.net header.b=uXSoyNvH; x-ptr=pass x-ptr-helo=mail.kernel.org x-ptr-lookup=mail.kernel.org; x-return-mx=pass smtp.domain=kernel.org smtp.result=pass smtp_is_org_domain=yes header.domain=kernel.org header.result=pass header_is_org_domain=yes; x-tls=pass version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128 X-Remote-Delivered-To: security@kernel.org DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 695C121737 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=htejun@gmail.com X-Google-Smtp-Source: AG47ELtR8WmJv+33U06M2my+oRYvML78zAjbpyVVKh0kxFgMmsi3u8DvQT1C3nu5zi1kbKWXCohvSg== Sender: Tejun Heo Date: Mon, 19 Mar 2018 09:45:23 -0700 From: Tejun Heo To: Lai Jiangshan Cc: Linus Torvalds , Jann Horn , "Paul E. McKenney" , Benjamin LaHaise , Al Viro , Kent Overstreet , security@kernel.org, LKML , kernel-team@fb.com Subject: Re: [PATCH 6/8] RCU, workqueue: Implement rcu_work Message-ID: <20180319164523.GB519464@devbig577.frc2.facebook.com> References: <20180314194205.1651587-1-tj@kernel.org> <20180314194515.1661824-1-tj@kernel.org> <20180314194515.1661824-6-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 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