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Thu, 23 Aug 2018 08:42:02 -0700 (PDT) Subject: Re: [PATCH] blk-wbt: get back the missed wakeup from __wbt_done To: Jianchao Wang Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <1535029718-17259-1-git-send-email-jianchao.w.wang@oracle.com> From: Jens Axboe Message-ID: <809b2243-7a76-3d8a-5d1b-b6b9d9712f41@kernel.dk> Date: Thu, 23 Aug 2018 09:42:01 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: <1535029718-17259-1-git-send-email-jianchao.w.wang@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/23/18 7:08 AM, Jianchao Wang wrote: > @@ -491,31 +525,27 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, > __acquires(lock) > { > struct rq_wait *rqw = get_rq_wait(rwb, wb_acct); > - DECLARE_WAITQUEUE(wait, current); > - bool has_sleeper; > - > - has_sleeper = wq_has_sleeper(&rqw->wait); > - if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw))) > + struct wait_queue_entry wait; > + struct wbt_wait_data data = { > + .curr = current, > + .rwb = rwb, > + .rqw = rqw, > + .rw = rw, > + }; > + > + if (!wq_has_sleeper(&rqw->wait) && > + rq_wait_inc_below(rqw, get_limit(rwb, rw))) > return; > > - add_wait_queue_exclusive(&rqw->wait, &wait); > - do { > - set_current_state(TASK_UNINTERRUPTIBLE); > - > - if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw))) > - break; > - > - if (lock) { > - spin_unlock_irq(lock); > - io_schedule(); > - spin_lock_irq(lock); > - } else > - io_schedule(); > - has_sleeper = false; > - } while (1); > - > - __set_current_state(TASK_RUNNING); > - remove_wait_queue(&rqw->wait, &wait); > + wbt_init_wait(&wait, &data); > + prepare_to_wait_exclusive(&rqw->wait, &wait, > + TASK_UNINTERRUPTIBLE); > + if (lock) { > + spin_unlock_irq(lock); > + io_schedule(); > + spin_lock_irq(lock); > + } else > + io_schedule(); Aren't we still missing a get-token attempt after adding to the waitqueue? For the case where someone frees the token after your initial check, but before you add yourself to the waitqueue. -- Jens Axboe