Re: [PATCH v3] f2fs: fix to keep isolation of atomic write

Chao Yu
2021-04-13T03:41:43Z

On 2021/4/13 11:27, Jaegeuk Kim wrote:
> On 04/12, Chao Yu wrote:
>> As Yi Chen reported, there is a potential race case described as below:
>>
>> Thread A Thread B
>> - f2fs_ioc_start_atomic_write
>> - mkwrite
>> - set_page_dirty
>> - f2fs_set_page_private(page, 0)
>> - set_inode_flag(FI_ATOMIC_FILE)
>> - mkwrite same page
>> - set_page_dirty
>> - f2fs_register_inmem_page
>> - f2fs_set_page_private(ATOMIC_WRITTEN_PAGE)
>> failed due to PagePrivate flag has been set
>> - list_add_tail
>> - truncate_inode_pages
>> - f2fs_invalidate_page
>> - clear page private but w/o remove it from
>> inmem_list
>> - set page->mapping to NULL
>> - f2fs_ioc_commit_atomic_write
>> - __f2fs_commit_inmem_pages
>> - __revoke_inmem_pages
>> - f2fs_put_page panic as page->mapping is NULL
>>
>> The root cause is we missed to keep isolation of atomic write in the case
>> of start_atomic_write vs mkwrite, let start_atomic_write helds i_mmap_sem
>> lock to avoid this issue.
>
> My only concern is performance regression. Could you please verify the numbers?

Do you have specific test script?

IIRC, the scenario you mean is multi-threads write/mmap the same db, right?

Thanks,

>
>>
>> Reported-by: Yi Chen <chenyi77@huawei.com>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>> v3:
>> - rebase to last dev branch
>> - update commit message because this patch fixes a different racing issue
>> of atomic write
>> fs/f2fs/file.c | 3 +++
>> fs/f2fs/segment.c | 6 ++++++
>> 2 files changed, 9 insertions(+)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index d697c8900fa7..6284b2f4a60b 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -2054,6 +2054,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> goto out;
>>
>> down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>>
>> /*
>> * Should wait end_io to count F2FS_WB_CP_DATA correctly by
>> @@ -2064,6 +2065,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> inode->i_ino, get_dirty_pages(inode));
>> ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
>> if (ret) {
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>> goto out;
>> }
>> @@ -2077,6 +2079,7 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>> /* add inode in inmem_list first and set atomic_file */
>> set_inode_flag(inode, FI_ATOMIC_FILE);
>> clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>
>> f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 0cb1ca88d4aa..78c8342f52fd 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -325,6 +325,7 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>> struct f2fs_inode_info *fi = F2FS_I(inode);
>>
>> do {
>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>> mutex_lock(&fi->inmem_lock);
>> if (list_empty(&fi->inmem_pages)) {
>> fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
>> @@ -339,11 +340,13 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>
>> mutex_unlock(&fi->inmem_lock);
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> break;
>> }
>> __revoke_inmem_pages(inode, &fi->inmem_pages,
>> true, false, true);
>> mutex_unlock(&fi->inmem_lock);
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> } while (1);
>> }
>>
>> @@ -468,6 +471,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>> f2fs_balance_fs(sbi, true);
>>
>> down_write(&fi->i_gc_rwsem[WRITE]);
>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>>
>> f2fs_lock_op(sbi);
>> set_inode_flag(inode, FI_ATOMIC_COMMIT);
>> @@ -479,6 +483,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>> clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>>
>> f2fs_unlock_op(sbi);
>> +
>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>> up_write(&fi->i_gc_rwsem[WRITE]);
>>
>> return err;
>> --
>> 2.29.2
> .
>