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Subject: Re: [f2fs-dev] [PATCH v2] f2fs: fix to keep isolation of atomic write
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
References: <20201230075557.108818-1-yuchao0@huawei.com>
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 <d146348b-3bbd-c1a5-72eb-b054cbcf0b13@huawei.com>
 <X/4jZY0bzkTCbDTY@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <240391d4-c3bb-882d-0e86-1e30e2fd0ef4@huawei.com>
Date:   Wed, 13 Jan 2021 09:30:21 +0800
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On 2021/1/13 6:32, Jaegeuk Kim wrote:
> On 01/12, Chao Yu wrote:
>> 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?
> 
> Nothing special. Just generating multiple sqlite transactions to the same db.

I doubt that start/commit flow race with ->release/->flush interface can cause
lower concurrency?

f2fs_ioc_start_atomic_write or			->release or ->flush
f2fs_ioc_commit_atomic_write
						 - f2fs_drop_inmem_pages
						  down_write(&F2FS_I(inode)->i_mmap_sem);
down_write(&F2FS_I(inode)->i_mmap_sem);

How about trying this testcase again after removing i_mmap_sem lock in
f2fs_drop_inmem_pages()?

Thanks,

> 
>>
>> 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
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Linux-f2fs-devel mailing list
>>>>> Linux-f2fs-devel@lists.sourceforge.net
>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>>
>>>>
>>>> _______________________________________________
>>>> Linux-f2fs-devel mailing list
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>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>> .
>>>
> .
>