Messages in this thread | | | Subject | Re: [PATCH] f2fs: avoid race between zero_range and background GC | From | Chao Yu <> | Date | Fri, 27 Jul 2018 20:16:50 +0800 |
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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.
> >> 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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