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Subject: Re: [PATCH v2] f2fs: fix to keep isolation of atomic write
To:     Jaegeuk Kim <jaegeuk@kernel.org>
CC:     <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-kernel@vger.kernel.org>, <chao@kernel.org>
References: <20201230075557.108818-1-yuchao0@huawei.com>
 <YAC9a6quO2VOirLi@google.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <3923906d-f208-f6c2-f121-5e77e8fb6b28@huawei.com>
Date:   Fri, 15 Jan 2021 15:59:03 +0800
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On 2021/1/15 5:53, Jaegeuk Kim wrote:
> 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
> 
> Hmm, how about removing fs/f2fs/trace.c to make private more complicated
> like this? I think we can get IO traces from tracepoints.

Hmm, actually, there is are issues, one is the trace IO, the other is the
race issue (atomic_start,commit,drop vs mkwrite) which can make isolation
semantics of transaction be broken.

Or can we avoid atomic file racing with file mmap?

- atomic_start			- file_mmap
				 - inode_lock
				 - if (FI_ATOMIC_FILE) return
  - inode_lock
  - if (FI_MMAP_FILE) return

Thanks,

> 
>> 					- 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
> .
>