Messages in this thread | | | Subject | Re: [PATCH] f2fs: avoid race between zero_range and background GC | From | Chao Yu <> | Date | Sun, 29 Jul 2018 10:53:58 +0800 |
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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
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