Date:   Sat, 27 Mar 2021 09:52:28 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH] Revert "f2fs: give a warning only for readonly
 partition"

On 2021/3/27 1:30, Jaegeuk Kim wrote:
> On 03/26, Chao Yu wrote:
>> On 2021/3/26 9:19, Jaegeuk Kim wrote:
>>> On 03/26, Chao Yu wrote:
>>>> On 2021/3/25 9:59, Chao Yu wrote:
>>>>> On 2021/3/25 6:44, Jaegeuk Kim wrote:
>>>>>> On 03/24, Chao Yu wrote:
>>>>>>> On 2021/3/24 12:22, Jaegeuk Kim wrote:
>>>>>>>> On 03/24, Chao Yu wrote:
>>>>>>>>> On 2021/3/24 2:39, Jaegeuk Kim wrote:
>>>>>>>>>> On 03/23, Chao Yu wrote:
>>>>>>>>>>> This reverts commit 938a184265d75ea474f1c6fe1da96a5196163789.
>>>>>>>>>>>
>>>>>>>>>>> Because that commit fails generic/050 testcase which expect failure
>>>>>>>>>>> during mount a recoverable readonly partition.
>>>>>>>>>>
>>>>>>>>>> I think we need to change generic/050, since f2fs can recover this partition,
>>>>>>>>>
>>>>>>>>> Well, not sure we can change that testcase, since it restricts all generic
>>>>>>>>> filesystems behavior. At least, ext4's behavior makes sense to me:
>>>>>>>>>
>>>>>>>>> 	journal_dev_ro = bdev_read_only(journal->j_dev);
>>>>>>>>> 	really_read_only = bdev_read_only(sb->s_bdev) | journal_dev_ro;
>>>>>>>>>
>>>>>>>>> 	if (journal_dev_ro && !sb_rdonly(sb)) {
>>>>>>>>> 		ext4_msg(sb, KERN_ERR,
>>>>>>>>> 			 "journal device read-only, try mounting with '-o ro'");
>>>>>>>>> 		err = -EROFS;
>>>>>>>>> 		goto err_out;
>>>>>>>>> 	}
>>>>>>>>>
>>>>>>>>> 	if (ext4_has_feature_journal_needs_recovery(sb)) {
>>>>>>>>> 		if (sb_rdonly(sb)) {
>>>>>>>>> 			ext4_msg(sb, KERN_INFO, "INFO: recovery "
>>>>>>>>> 					"required on readonly filesystem");
>>>>>>>>> 			if (really_read_only) {
>>>>>>>>> 				ext4_msg(sb, KERN_ERR, "write access "
>>>>>>>>> 					"unavailable, cannot proceed "
>>>>>>>>> 					"(try mounting with noload)");
>>>>>>>>> 				err = -EROFS;
>>>>>>>>> 				goto err_out;
>>>>>>>>> 			}
>>>>>>>>> 			ext4_msg(sb, KERN_INFO, "write access will "
>>>>>>>>> 			       "be enabled during recovery");
>>>>>>>>> 		}
>>>>>>>>> 	}
>>>>>>>>>
>>>>>>>>>> even though using it as readonly. And, valid checkpoint can allow for user to
>>>>>>>>>> read all the data without problem.
>>>>>>>>>
>>>>>>>>>>>        		if (f2fs_hw_is_readonly(sbi)) {
>>>>>>>>>
>>>>>>>>> Since device is readonly now, all write to the device will fail, checkpoint can
>>>>>>>>> not persist recovered data, after page cache is expired, user can see stale data.
>>>>>>>>
>>>>>>>> My point is, after mount with ro, there'll be no data write which preserves the
>>>>>>>> current status. So, in the next time, we can recover fsync'ed data later, if
>>>>>>>> user succeeds to mount as rw. Another point is, with the current checkpoint, we
>>>>>>>> should not have any corrupted metadata. So, why not giving a chance to show what
>>>>>>>> data remained to user? I think this can be doable only with CoW filesystems.
>>>>>>>
>>>>>>> I guess we're talking about the different things...
>>>>>>>
>>>>>>> Let me declare two different readonly status:
>>>>>>>
>>>>>>> 1. filesystem readonly: file system is mount with ro mount option, and
>>>>>>> app from userspace can not modify any thing of filesystem, but filesystem
>>>>>>> itself can modify data on device since device may be writable.
>>>>>>>
>>>>>>> 2. device readonly: device is set to readonly status via 'blockdev --setro'
>>>>>>> command, and then filesystem should never issue any write IO to the device.
>>>>>>>
>>>>>>> So, what I mean is, *when device is readonly*, rather than f2fs mountpoint
>>>>>>> is readonly (f2fs_hw_is_readonly() returns true as below code, instead of
>>>>>>> f2fs_readonly() returns true), in this condition, we should not issue any
>>>>>>> write IO to device anyway, because, AFAIK, write IO will fail due to
>>>>>>> bio_check_ro() check.
>>>>>>
>>>>>> In that case, mount(2) will try readonly, no?
>>>>>
>>>>> Yes, if device is readonly, mount (2) can not mount/remount device to rw
>>>>> mountpoint.
>>>>
>>>> Any other concern about this patch?
>>>
>>> Indeed we're talking about different things. :)
>>>
>>> This case is mount(ro) with device(ro) having some data to recover.
>>> My point is why not giving a chance to mount(ro) to show the current data
>>> covered by a valid checkpoint. This doesn't change anything in the disk,
>> Got your idea.
>>
>> IMO, it has potential issue in above condition:
>>
>>>>>>>>> Since device is readonly now, all write to the device will fail, checkpoint can
>>>>>>>>> not persist recovered data, after page cache is expired, user can see stale data.
>>
>> e.g.
>>
>> Recovery writes one inode and then triggers a checkpoint, all writes fail
> 
> I'm confused. Currently we don't trigger the roll-forward recovery.

Oh, my miss, sorry. :-P

My point is in this condition we can return error and try to notice user to
mount with disable_roll_forward or norecovery option, then at least user can
know he should not expect last fsynced data in newly mounted image.

Or we can use f2fs_recover_fsync_data() to check whether there is fsynced data,
if there is no such data, then let mount() succeed.

Thanks,

> 
>> due to device is readonly, once inode cache is reclaimed by vm, user will see
>> old inode when reloading it, or even see corrupted fs if partial meta inode's
>> cache is expired.
>>
>> Thoughts?
>>
>> Thanks,
>>
>>> and in the next time, it allows mount(rw|ro) with device(rw) to recover
>>> the data seamlessly.
>>>
>>>>
>>>> Thanks,
>>>>
>>>>>
>>>>> Thanks,
>>>>>
>>>>>>
>>>>>> # blockdev --setro /dev/vdb
>>>>>> # mount -t f2fs /dev/vdb /mnt/test/
>>>>>> mount: /mnt/test: WARNING: source write-protected, mounted read-only.
>>>>>>
>>>>>>>
>>>>>>>      		if (f2fs_hw_is_readonly(sbi)) {
>>>>>>> -			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
>>>>>>> -				err = -EROFS;
>>>>>>> +			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG))
>>>>>>>      				f2fs_err(sbi, "Need to recover fsync data, but write access unavailable");
>>>>>>> -				goto free_meta;
>>>>>>> -			}
>>>>>>> -			f2fs_info(sbi, "write access unavailable, skipping recovery");
>>>>>>> +			else
>>>>>>> +				f2fs_info(sbi, "write access unavailable, skipping recovery");
>>>>>>>      			goto reset_checkpoint;
>>>>>>>      		}
>>>>>>>
>>>>>>> For the case of filesystem is readonly and device is writable, it's fine
>>>>>>> to do recovery in order to let user to see fsynced data.
>>>>>>>
>>>>>>> Thanks,
>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>> Am I missing something?
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Fixes: 938a184265d7 ("f2fs: give a warning only for readonly partition")
>>>>>>>>>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>>>>>>>>>> ---
>>>>>>>>>>>        fs/f2fs/super.c | 8 +++++---
>>>>>>>>>>>        1 file changed, 5 insertions(+), 3 deletions(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>>>>>>>>>> index b48281642e98..2b78ee11f093 100644
>>>>>>>>>>> --- a/fs/f2fs/super.c
>>>>>>>>>>> +++ b/fs/f2fs/super.c
>>>>>>>>>>> @@ -3952,10 +3952,12 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>>>>>>>>>>>        		 * previous checkpoint was not done by clean system shutdown.
>>>>>>>>>>>        		 */
>>>>>>>>>>>        		if (f2fs_hw_is_readonly(sbi)) {
>>>>>>>>>>> -			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG))
>>>>>>>>>>> +			if (!is_set_ckpt_flags(sbi, CP_UMOUNT_FLAG)) {
>>>>>>>>>>> +				err = -EROFS;
>>>>>>>>>>>        				f2fs_err(sbi, "Need to recover fsync data, but write access unavailable");
>>>>>>>>>>> -			else
>>>>>>>>>>> -				f2fs_info(sbi, "write access unavailable, skipping recovery");
>>>>>>>>>>> +				goto free_meta;
>>>>>>>>>>> +			}
>>>>>>>>>>> +			f2fs_info(sbi, "write access unavailable, skipping recovery");
>>>>>>>>>>>        			goto reset_checkpoint;
>>>>>>>>>>>        		}
>>>>>>>>>>> -- 
>>>>>>>>>>> 2.29.2
>>>>>>>>>> .
>>>>>>>>>>
>>>>>>>> .
>>>>>>>>
>>>>>> .
>>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Linux-f2fs-devel mailing list
>>>>> Linux-f2fs-devel@...ts.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>> .
>>>>>
>>> .
>>>
> .
> 

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