Re: [f2fs-dev] [PATCH 1/3] f2fs: turn off atomic writes when deteting abnormal behaviors

[Chao Yu]

On 2018/7/27 17:17, Jaegeuk Kim wrote:
> On 07/23, Chao Yu wrote:
>> On 2018/7/23 21:03, Jaegeuk Kim wrote:
>>> On 07/16, Chao Yu wrote:
>>>> On 2018/7/15 9:11, Jaegeuk Kim wrote:
>>>>> In order to prevent abusing atomic writes by abnormal users, we've added a
>>>>> threshold, 20% over memory footprint, which disallows further atomic writes.
>>>>> Previously, however, SQLite doesn't know the files became normal, so that
>>>>> it could write stale data and commit on revoked normal database file.
>>>>>
>>>>> Once f2fs detects such the abnormal behavior, this patch simply disables
>>>>> all the atomic operations such as:
>>>>> - write_begin() gives EINVAL to avoid stale data writes, and SQLite will call
>>>>>   F2FS_IOC_ABORT_VOLATILE_WRITE to notify aborting the transaction,
>>>>> - F2FS_IOC_START_ATOMIC_WRITE gives EINVAL for SQLite to fall back normal
>>>>>   journal_mode,
>>>>> - F2FS_IOC_COMMIT_ATOMIC_WRITE gives EINVAL, if the file was revoked, so that
>>>>>   Framework retries to submit the transaction given propagated SQLite error.
>>>>>
>>>>> Note that, this patch also turns off atomic operations, if foreground GC tries
>>>>> to move atomic files too frequently.
>>>>
>>>> Well, how about just keeping original implementation: shutdown atomic write for
>>>> those files which are really affect fggc? Since intention of the original
>>>> behavior is targeting to abnormal atomic write usage, e.g. open atomic_write
>>>> file for very long time, then fggc will be blocked each time when moving its
>>>> block. So shutdown it, fggc will recover.
>>>
>>> The point here is stopping sqlite to keep going wrong data writes even after
>>> we already revoked blocks.
>>
>> Yes, that's correct, what I mean is that if we can do that with smaller
>> granularity like just revoke blocks for file which is blocking fggc, it will
>> affect system/sqlite flow much less than forcing closing all atomic_write.
> 
> How about this?

Yes, it looks good to me. :)

> 
> From 64d2becb82a496c2e2c04abeed42efa3b401ee20 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> Date: Fri, 27 Jul 2018 18:15:11 +0900
> Subject: [PATCH] f2fs: don't allow any writes on aborted atomic writes
> 
> In order to prevent abusing atomic writes by abnormal users, we've added a
> threshold, 20% over memory footprint, which disallows further atomic writes.
> Previously, however, SQLite doesn't know the files became normal, so that
> it could write stale data and commit on revoked normal database file.
> 
> Once f2fs detects such the abnormal behavior, this patch tries to avoid further
> writes in write_begin().
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>

Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>

Thanks,

> ---
>  fs/f2fs/data.c | 3 ++-
>  fs/f2fs/file.c | 7 ++++++-
>  2 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 22dd00c6e241..02ec2603725f 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2295,7 +2295,8 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
>  	trace_f2fs_write_begin(inode, pos, len, flags);
>  
>  	if (f2fs_is_atomic_file(inode) &&
> -			!f2fs_available_free_memory(sbi, INMEM_PAGES)) {
> +			(is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST) ||
> +			!f2fs_available_free_memory(sbi, INMEM_PAGES))) {
>  		err = -ENOMEM;
>  		drop_atomic = true;
>  		goto fail;
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index ff2cb8fb6934..c2c47f3248c4 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1708,8 +1708,11 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>  
>  	down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>  
> -	if (f2fs_is_atomic_file(inode))
> +	if (f2fs_is_atomic_file(inode)) {
> +		if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
> +			ret = -EINVAL;
>  		goto out;
> +	}
>  
>  	ret = f2fs_convert_inline_inode(inode);
>  	if (ret)
> @@ -1871,6 +1874,8 @@ static int f2fs_ioc_abort_volatile_write(struct file *filp)
>  		ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
>  	}
>  
> +	clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> +
>  	inode_unlock(inode);
>  
>  	mnt_drop_write_file(filp);
>