Subject: Re: [PATCH v2 1/5] ext4: Fix reusing stale buffer heads from last
 failed mounting
To:     Jan Kara <jack@suse.cz>
CC:     <tytso@mit.edu>, <adilger.kernel@dilger.ca>, <jack@suse.com>,
        <tudor.ambarus@linaro.org>, <linux-ext4@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
References: <20230313132021.672134-1-chengzhihao1@huawei.com>
 <20230313132021.672134-2-chengzhihao1@huawei.com>
 <20230314113342.74g2pfwe5y7b5poa@quack3>
 <b7d108d6-9e5a-d88a-305d-932e75098b09@huawei.com>
 <20230314121125.tnz22hckcaj46kp6@quack3>
From:   Zhihao Cheng <chengzhihao1@huawei.com>
Message-ID: <f86584f6-3877-ff18-47a1-2efaa12d18b2@huawei.com>
Date:   Tue, 14 Mar 2023 20:31:43 +0800
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> On Tue 14-03-23 20:01:46, Zhihao Cheng wrote:
>> 在 2023/3/14 19:33, Jan Kara 写道:
>> Hi Jan,
>>
>>>
>>>> @@ -1271,14 +1277,8 @@ static void ext4_put_super(struct super_block *sb)
>>>>    	sync_blockdev(sb->s_bdev);
>>>>    	invalidate_bdev(sb->s_bdev);
>>
>> For journal in the inode case, journal bhs come from block device, which
>> means buffers will be dropped after this line 'invalidate_bdev(sb->s_bdev)'
>> being executed.
> 
> Right, I've missed that. But then why do you remove the sbi->s_journal_bdev
> != sb->s_bdev condition below?
> 

I think 'sbi->s_journal_bdev != sb->s_bdev' always becomes true if 
sbi->s_journal_bdev exists.


mount_bdev
  fmode_t mode = FMODE_READ | FMODE_EXCL
  bdev_a = blkdev_get_by_path(dev_name, mode, fs_type)


mount_bdev->ext4_fill_super->ext4_load_and_init_journal->ext4_load_journal->ext4_get_dev_journal:
  bdev_b = ext4_blkdev_get(j_dev, sb)
   bdev_b = blkdev_get_by_dev(dev, FMODE_READ|FMODE_WRITE|FMODE_EXCL, sb)
  EXT4_SB(sb)->s_journal_bdev = bdev_b


bdev_a cannot be bdev_b, because bd_prepare_to_claim() makes sure the 
same block device cannot be openned twice with mode 'FMODE_EXCL'.