linux-ext4 - Re: [PATCH v2 3/5] ext4: detect metadata async write error when getting journal's write access

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Message-ID: <8caf9fe1-b7ce-655f-1f4d-3e0e90e211dc@huawei.com>
Date:   Wed, 17 Jun 2020 21:44:35 +0800
From:   "zhangyi (F)" <yi.zhang@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <zhangxiaoxu5@...wei.com>,
        <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] ext4: detect metadata async write error when
 getting journal's write access

On 2020/6/17 20:41, Jan Kara wrote:
> On Wed 17-06-20 19:59:45, zhangyi (F) wrote:
>> Although we have already introduce s_bdev_wb_err_work to detect and
>> handle async write metadata buffer error as soon as possible, there is
>> still a potential race that could lead to filesystem inconsistency,
>> which is the buffer may reading and re-writing out to journal before
>> s_bdev_wb_err_work run. So this patch detect bdev mapping->wb_err when
>> getting journal's write access and also mark the filesystem error if
>> something bad happened.
>>
>> Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>
> 
> So instead of all this, cannot we just do:
> 
> 	if (work_pending(sbi->s_bdev_wb_err_work))
> 		flush_work(sbi->s_bdev_wb_err_work);
> 
> ? And so we are sure the filesystem is aborted if the abort was pending?
> 

Thanks for this suggestion. Yeah, we could do this, it depends on the second
patch, if we check and flush the pending work here, we could not use the
end_buffer_async_write() in ext4_end_buffer_async_write(), we need to open
coding ext4_end_buffer_async_write() and queue the error work before the
buffer is unlocked, or else the race is still there. Do you agree ?

Thanks,
Yi.