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Mon, 27 Aug 2018 06:14:32 +0000 Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id w7R6ERIw031835 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 27 Aug 2018 06:14:27 GMT Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id w7R6EQqb010222; Mon, 27 Aug 2018 06:14:26 GMT Received: from [10.182.70.180] (/10.182.70.180) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sun, 26 Aug 2018 23:14:26 -0700 Subject: Re: [PATCH] blk-wbt: get back the missed wakeup from __wbt_done To: Jens Axboe , Anchal Agarwal Cc: fllinden@amazon.com, "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" References: <1535029718-17259-1-git-send-email-jianchao.w.wang@oracle.com> <20180823210144.GB5624@kaos-source-ops-60001.pdx1.amazon.com> <3eaa20ce-0599-c405-d979-87d91ea331d2@kernel.dk> <20180824181223.GA9049@kaos-source-ops-60001.pdx1.amazon.com> <677c8648-63fd-601c-b906-40a8502f9782@kernel.dk> <20180824203305.GA4690@kaos-source-ops-60001.pdx1.amazon.com> <2fecf2f2-f00b-f6ba-710a-54ceaacfedbb@kernel.dk> <00445460-d826-4d85-c5f4-fa565892da01@oracle.com> From: "jianchao.wang" Message-ID: <3876c36c-fec6-6586-435f-dc177dc38c76@oracle.com> Date: Mon, 27 Aug 2018 14:15:07 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <00445460-d826-4d85-c5f4-fa565892da01@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8997 signatures=668707 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1808270066 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/27/2018 11:52 AM, jianchao.wang wrote: > Hi Jens > > On 08/25/2018 11:41 PM, Jens Axboe wrote: >> do { >> - set_current_state(TASK_UNINTERRUPTIBLE); >> + if (test_bit(0, &data.flags)) >> + break; >> >> - if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw))) >> + WARN_ON_ONCE(list_empty(&data.wq.entry)); >> + >> + if (!has_sleeper && >> + rq_wait_inc_below(rqw, get_limit(rwb, rw))) { >> + finish_wait(&rqw->wait, &data.wq); >> + >> + /* >> + * We raced with wbt_wake_function() getting a token, >> + * which means we now have two. Put ours and wake >> + * anyone else potentially waiting for one. >> + */ >> + if (test_bit(0, &data.flags)) >> + wbt_rqw_done(rwb, rqw, wb_acct); >> break; > > Just use 'bool' variable should be OK > After finish_wait, no one could race with us here. > >> + } >> >> if (lock) { >> spin_unlock_irq(lock); >> @@ -511,11 +569,11 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, >> spin_lock_irq(lock); >> } else >> io_schedule(); >> + >> has_sleeper = false; >> } while (1); > > I cannot get the point of "since we can't rely on just being woken from the ->func handler > we set". > Do you mean there could be someone else could wake up this task ? > If we do need a recheck after the io_schedule, we could do as following: static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct, unsigned long rw, spinlock_t *lock) __releases(lock) __acquires(lock) { struct rq_wait *rqw = get_rq_wait(rwb, wb_acct); struct wbt_wait_data data = { .wq = { .func = wbt_wake_function, .entry = LIST_HEAD_INIT(data.wq.entry), }, .curr = current, .rwb = rwb, .rqw = rqw, .rw = rw, }; bool has_sleeper; bool got = false; retry: has_sleeper = wq_has_sleeper(&rqw->wait); if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw))) return; prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE); if (!has_sleeper && rq_wait_inc_below(rqw, get_limit(rwb, rw))) { got = true; goto out; } if (lock) { spin_unlock_irq(lock); io_schedule(); spin_lock_irq(lock); } else io_schedule(); out: finish_wait(&rqw->wait, &data.wq); /* * We raced with wbt_wake_function() getting a token, * which means we now have two. Put ours and wake * anyone else potentially waiting for one. */ if (data.got && got) wbt_rqw_done(rwb, rqw, wb_acct); else if (!data.got && !got) goto retry; Thanks Jianchao