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

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Date:   Tue, 13 Apr 2021 11:41:32 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>,
        Yi Chen <chenyi77@...wei.com>
Subject: Re: [PATCH v3] f2fs: fix to keep isolation of atomic write

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@...wei.com>
>> Signed-off-by: Chao Yu <yuchao0@...wei.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
> .
>