lkml.org 
[lkml]   [2018]   [Jul]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] f2fs: avoid race between zero_range and background GC
From
Date
On 2018/7/29 10:02, Jaegeuk Kim wrote:
> On 07/27, Chao Yu wrote:
>> On 2018/7/27 18:29, Jaegeuk Kim wrote:
>>> On 07/26, Chao Yu wrote:
>>>> Thread A Background GC
>>>> - f2fs_zero_range
>>>> - truncate_pagecache_range
>>>> - gc_data_segment
>>>> - get_read_data_page
>>>> - move_data_page
>>>> - set_page_dirty
>>>> - set_cold_data
>>>> - f2fs_do_zero_range
>>>> - dn->data_blkaddr = NEW_ADDR;
>>>> - f2fs_set_data_blkaddr
>>>>
>>>> Actually, we don't need to set dirty & checked flag on the page, since
>>>> all valid data in the page should be zeroed by zero_range().
>>>
>>> But, it doesn't matter too much, right?
>>
>> No, if the dirtied page is writebacked after f2fs_do_zero_range(), result of
>> zero_range() should be wrong, as zeroed page contains valid user data.
>
> How about truncating page caches after block address change or doing it twice
> before and after?

Thread A Background GC
- f2fs_zero_range
- truncate_pagecache_range
- gc_data_segment
- get_read_data_page
- move_data_page
- set_page_dirty
- set_cold_data
- f2fs_do_zero_range
- dn->data_blkaddr = NEW_ADDR;
- f2fs_set_data_blkaddr
bdi-flusher
- __write_data_page
- f2fs_update_data_blkaddr
: data_blkaddr has been updated here.
- truncate_pagecache_range
: data & dnode has been writebacked before page cache truncation?

How about this case?

Thanks,

>
>>
>>>
>>>> Use i_gc_rwsem[WRITE] to avoid such race condition.
>>>
>>> Hope to avoid abusing i_gc_rwsem[] tho.
>>
>> Agreed, let's try avoiding until we have to use it.
>>
>> Thanks,
>>
>>>
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>> ---
>>>> fs/f2fs/file.c | 2 ++
>>>> 1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 267ec3794e1e..7bd2412a8c37 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -1309,6 +1309,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
>>>> if (ret)
>>>> return ret;
>>>>
>>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> ret = filemap_write_and_wait_range(mapping, offset, offset + len - 1);
>>>> if (ret)
>>>> @@ -1389,6 +1390,7 @@ static int f2fs_zero_range(struct inode *inode, loff_t offset, loff_t len,
>>>> }
>>>> out_sem:
>>>> up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>>
>>>> return ret;
>>>> }
>>>> --
>>>> 2.18.0.rc1

\
 
 \ /
  Last update: 2018-07-29 04:54    [W:0.057 / U:1.084 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site