linux-kernel - Re: [PATCH] blk-wbt: get back the missed wakeup from __wbt

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Message-ID: <cc7b19f7-b5c5-e89d-eb12-cdff6e35fb4d@kernel.dk>
Date:   Mon, 27 Aug 2018 09:37:47 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "jianchao.wang" <jianchao.w.wang@...cle.com>,
        Anchal Agarwal <anchalag@...n.com>
Cc:     fllinden@...zon.com,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] blk-wbt: get back the missed wakeup from __wbt_done

On 8/26/18 9:52 PM, 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.

I was mostly concerned with the check post prep_to_wait(), but since the
spin unlock should include a barrier, the bool should actually be enough.
I'll change that back once I test.

-- 
Jens Axboe