Re: [PATCH 3/4] f2fs: fix avoid race between truncate and background GC

[Chao Yu <chao@kernel.org>]

On 2018/7/29 14:13, Jaegeuk Kim wrote:
> On 07/29, Chao Yu wrote:
>> On 2018/7/29 9:58, Jaegeuk Kim wrote:
>>> On 07/27, Chao Yu wrote:
>>>> Thread A				Background GC
>>>> - f2fs_setattr isize to 0
>>>>  - truncate_setsize
>>>> 					- gc_data_segment
>>>> 					 - f2fs_get_read_data_page page #0
>>>> 					  - set_page_dirty
>>>> 					  - set_cold_data
>>>>  - f2fs_truncate
>>>>
>>>> - f2fs_setattr isize to 4k
>>>> - read 4k <--- hit data in cached page #0
>>>>
>>>> Above race condition can cause read out invalid data in a truncated
>>>> page, fix it by i_gc_rwsem[WRITE] lock.
>>>
>>> We can truncate pages again after f2fs_truncate()?
>>
>> I think it can fix this issue, although it looks a little strange to truncate
>> page cache twice.
> 
> It'd be fine to do setsize first, and drop the cache later.

Let me rethink about this solution, since we have different case like punch_hole
which may not need setsize.

Thanks,

> 
>>
>> Thanks,
>>
>>>
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>> ---
>>>>  fs/f2fs/data.c |  4 ++++
>>>>  fs/f2fs/file.c | 33 +++++++++++++++++++--------------
>>>>  2 files changed, 23 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index 071224ded5f4..a29f3162b887 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -2214,10 +2214,14 @@ static void f2fs_write_failed(struct address_space *mapping, loff_t to)
>>>>  	loff_t i_size = i_size_read(inode);
>>>>  
>>>>  	if (to > i_size) {
>>>> +		down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>  		down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +
>>>>  		truncate_pagecache(inode, i_size);
>>>>  		f2fs_truncate_blocks(inode, i_size, true);
>>>> +
>>>>  		up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>  	}
>>>>  }
>>>>  
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 7bd2412a8c37..ed5c9b0e0d0c 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -796,22 +796,25 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
>>>>  	}
>>>>  
>>>>  	if (attr->ia_valid & ATTR_SIZE) {
>>>> -		if (attr->ia_size <= i_size_read(inode)) {
>>>> -			down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> -			truncate_setsize(inode, attr->ia_size);
>>>> +		bool to_smaller = (attr->ia_size <= i_size_read(inode));
>>>> +
>>>> +		down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> +		down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +
>>>> +		truncate_setsize(inode, attr->ia_size);
>>>> +
>>>> +		if (to_smaller)
>>>>  			err = f2fs_truncate(inode);
>>>> -			up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> -			if (err)
>>>> -				return err;
>>>> -		} else {
>>>> -			/*
>>>> -			 * do not trim all blocks after i_size if target size is
>>>> -			 * larger than i_size.
>>>> -			 */
>>>> -			down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> -			truncate_setsize(inode, attr->ia_size);
>>>> -			up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +		/*
>>>> +		 * do not trim all blocks after i_size if target size is
>>>> +		 * larger than i_size.
>>>> +		 */
>>>> +		up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +		up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> +		if (err)
>>>> +			return err;
>>>>  
>>>> +		if (!to_smaller) {
>>>>  			/* should convert inline inode here */
>>>>  			if (!f2fs_may_inline_data(inode)) {
>>>>  				err = f2fs_convert_inline_inode(inode);
>>>> @@ -958,6 +961,7 @@ static int punch_hole(struct inode *inode, loff_t offset, loff_t len)
>>>>  
>>>>  			blk_start = (loff_t)pg_start << PAGE_SHIFT;
>>>>  			blk_end = (loff_t)pg_end << PAGE_SHIFT;
>>>> +			down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>  			down_write(&F2FS_I(inode)->i_mmap_sem);
>>>>  			truncate_inode_pages_range(mapping, blk_start,
>>>>  					blk_end - 1);
>>>> @@ -966,6 +970,7 @@ static int punch_hole(struct inode *inode, loff_t offset, loff_t len)
>>>>  			ret = f2fs_truncate_hole(inode, pg_start, pg_end);
>>>>  			f2fs_unlock_op(sbi);
>>>>  			up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +			up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>  		}
>>>>  	}
>>>>  
>>>> -- 
>>>> 2.18.0.rc1