Re: [f2fs-dev] [PATCH v2] f2fs: fix to keep isolation of atomic write

[Chao Yu <yuchao0@huawei.com>]

On 2021/1/12 0:32, Jaegeuk Kim wrote:
> On 01/06, Jaegeuk Kim wrote:
>> On 01/06, Jaegeuk Kim wrote:
>>> Hi Chao,
>>>
>>> With a quick test, this patch causes down_write failure resulting in blocking
>>> process. I didn't dig in the bug so, please check the code again. :P
>>
>> nvm. I can see it works now.
> 
> Hmm, this gives a huge perf regression when running sqlite. :(
> We may need to check the lock coverage. Thoughts?

I added i_mmap_sem lock only, so it can cause atomic_{start,commit,finish}
race with mmap and truncation operations in additionally.

I'd like to know what's your sqlite testcase?

Thanks,

> 
>>
>>>
>>> On 12/30, Chao Yu wrote:
>>>> ThreadA					ThreadB
>>>> - f2fs_ioc_start_atomic_write
>>>> - write
>>>> - f2fs_ioc_commit_atomic_write
>>>>   - f2fs_commit_inmem_pages
>>>>   - f2fs_drop_inmem_pages
>>>>   - f2fs_drop_inmem_pages
>>>>    - __revoke_inmem_pages
>>>> 					- f2fs_vm_page_mkwrite
>>>> 					 - set_page_dirty
>>>> 					  - tag ATOMIC_WRITTEN_PAGE and add page
>>>> 					    to inmem_pages list
>>>>    - clear_inode_flag(FI_ATOMIC_FILE)
>>>> 					- f2fs_vm_page_mkwrite
>>>> 					  - set_page_dirty
>>>> 					   - f2fs_update_dirty_page
>>>> 					    - f2fs_trace_pid
>>>> 					     - tag inmem page private to pid
>>>> 					- truncate
>>>> 					 - f2fs_invalidate_page
>>>> 					 - set page->mapping to NULL
>>>> 					  then it will cause panic once we
>>>> 					  access page->mapping
>>>>
>>>> The root cause is we missed to keep isolation of atomic write in the case
>>>> of commit_atomic_write vs mkwrite, let commit_atomic_write helds i_mmap_sem
>>>> lock to avoid this issue.
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>> ---
>>>> v2:
>>>> - use i_mmap_sem to avoid mkwrite racing with below flows:
>>>>   * f2fs_ioc_start_atomic_write
>>>>   * f2fs_drop_inmem_pages
>>>>   * f2fs_commit_inmem_pages
>>>>
>>>>   fs/f2fs/file.c    | 3 +++
>>>>   fs/f2fs/segment.c | 7 +++++++
>>>>   2 files changed, 10 insertions(+)
>>>>
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 4e6d4b9120a8..a48ec650d691 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -2050,6 +2050,7 @@ 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
>>>> @@ -2060,6 +2061,7 @@ 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;
>>>>   	}
>>>> @@ -2073,6 +2075,7 @@ 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 d8570b0359f5..dab870d9faf6 100644
>>>> --- a/fs/f2fs/segment.c
>>>> +++ b/fs/f2fs/segment.c
>>>> @@ -327,6 +327,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>>>>   	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>>>   	struct f2fs_inode_info *fi = F2FS_I(inode);
>>>>   
>>>> +	down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +
>>>>   	while (!list_empty(&fi->inmem_pages)) {
>>>>   		mutex_lock(&fi->inmem_lock);
>>>>   		__revoke_inmem_pages(inode, &fi->inmem_pages,
>>>> @@ -344,6 +346,8 @@ void f2fs_drop_inmem_pages(struct inode *inode)
>>>>   		sbi->atomic_files--;
>>>>   	}
>>>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>>> +
>>>> +	up_write(&F2FS_I(inode)->i_mmap_sem);
>>>>   }
>>>>   
>>>>   void f2fs_drop_inmem_page(struct inode *inode, struct page *page)
>>>> @@ -467,6 +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);
>>>> @@ -478,6 +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
>>>
>>>
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>>
>>
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