linux-kernel - Re: [PATCH v2 3/9] block: WARN if bdev inflight counter is negative

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Message-ID: <6bb64a49-a8db-3431-537f-913982886ba9@huaweicloud.com>
Date: Tue, 29 Apr 2025 09:43:12 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: John Garry <john.g.garry@...cle.com>, Yu Kuai <yukuai1@...weicloud.com>,
 hch@...radead.org, axboe@...nel.dk, xni@...hat.com, agk@...hat.com,
 snitzer@...nel.org, mpatocka@...hat.com, song@...nel.org, cl@...ux.com,
 nadav.amit@...il.com, ubizjak@...il.com, akpm@...ux-foundation.org
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 dm-devel@...ts.linux.dev, linux-raid@...r.kernel.org, yi.zhang@...wei.com,
 yangerkun@...wei.com, johnny.chenyi@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2 3/9] block: WARN if bdev inflight counter is negative

Hi,

在 2025/04/28 22:06, John Garry 写道:
> On 27/04/2025 09:29, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> Which means there is a BUG
> 
> nit: to me, BUG means symbol BUG(), and not a software bug (which I 
> think that you mean)

Actually, I mean the bio-based disk driver or blk-mq messed up the IO
accounting, IO done is more than IO start, and this is a bug.
> 
>> for related bio-based disk driver, or blk-mq
>> for rq-based disk, it's better not to hide the BUG.
> 
> AFICS, this check was not present for mq, so is it really required now? 
> I suppose that the code is simpler to always have the check. I find it 
> an odd check to begin with...

This check do present for mq, for example, diskstats_show() and
update_io_ticks().

Thanks,
Kuai

> 
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>>   block/genhd.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/block/genhd.c b/block/genhd.c
>> index f671d9ee00c4..d158c25237b6 100644
>> --- a/block/genhd.c
>> +++ b/block/genhd.c
>> @@ -136,9 +136,9 @@ static void part_in_flight_rw(struct block_device 
>> *part,
>>           inflight[0] += part_stat_local_read_cpu(part, in_flight[0], 
>> cpu);
>>           inflight[1] += part_stat_local_read_cpu(part, in_flight[1], 
>> cpu);
>>       }
>> -    if ((int)inflight[0] < 0)
>> +    if (WARN_ON_ONCE((int)inflight[0] < 0))
>>           inflight[0] = 0;
>> -    if ((int)inflight[1] < 0)
>> +    if (WARN_ON_ONCE((int)inflight[1] < 0))
>>           inflight[1] = 0;
>>   }
> 
> 
> .
>