Re: [PATCH] f2fs: refactor ->page_mkwrite() flow

[Chao Yu <yuchao0@huawei.com>]

On 2018/9/27 13:05, Jaegeuk Kim wrote:
> This makes xfstests/083 stuck. So, I'll drop it for a while.

Alright, let me check that case again.

Thanks,

> 
> On 09/26, Chao Yu wrote:
>> From: Chao Yu <yuchao0@huawei.com>
>>
>> Thread A				Thread B
>> - f2fs_vm_page_mkwrite
>> 					- f2fs_setattr
>> 					 - down_write(i_mmap_sem)
>> 					 - truncate_setsize
>> 					 - f2fs_truncate
>> 					 - up_write(i_mmap_sem)
>>  - f2fs_reserve_block
>>  reserve NEW_ADDR
>>  - skip dirty page due to truncation
>>
>> 1. we don't need to rserve new block address for a truncated page.
>> 2. dn.data_blkaddr is used out of node page lock coverage.
>>
>> Refactor ->page_mkwrite() flow to fix above issues:
>> - use __do_map_lock() to avoid racing checkpoint()
>> - lock data page in prior to dnode page
>> - cover f2fs_reserve_block with i_mmap_sem lock
>> - access dn.data_blkaddr under dnode lock
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>>  fs/f2fs/file.c | 29 ++++++++++++++---------------
>>  1 file changed, 14 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index 6f02c8daff76..fcb4788b48aa 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -47,7 +47,7 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>  	struct page *page = vmf->page;
>>  	struct inode *inode = file_inode(vmf->vma->vm_file);
>>  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>> -	struct dnode_of_data dn;
>> +	struct dnode_of_data dn = { .node_changed = false };
>>  	int err;
>>  
>>  	if (unlikely(f2fs_cp_error(sbi))) {
>> @@ -59,19 +59,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>  
>>  	f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
>>  
>> -	/* block allocation */
>> -	f2fs_lock_op(sbi);
>> -	set_new_dnode(&dn, inode, NULL, NULL, 0);
>> -	err = f2fs_reserve_block(&dn, page->index);
>> -	if (err) {
>> -		f2fs_unlock_op(sbi);
>> -		goto out;
>> -	}
>> -	f2fs_put_dnode(&dn);
>> -	f2fs_unlock_op(sbi);
>> -
>> -	f2fs_balance_fs(sbi, dn.node_changed);
>> -
>>  	file_update_time(vmf->vma->vm_file);
>>  	down_read(&F2FS_I(inode)->i_mmap_sem);
>>  	lock_page(page);
>> @@ -108,12 +95,24 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>  	/* fill the page */
>>  	f2fs_wait_on_page_writeback(page, DATA, false);
>>  
>> +	/* block allocation */
>> +	__do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, true);
>> +	set_new_dnode(&dn, inode, NULL, NULL, 0);
>> +	err = f2fs_reserve_block(&dn, page->index);
>> +	if (err)
>> +		goto out_unlock;
>> +
>>  	/* wait for GCed page writeback via META_MAPPING */
>>  	f2fs_wait_on_block_writeback(inode, dn.data_blkaddr);
>>  
>> +	f2fs_put_dnode(&dn);
>> +out_unlock:
>> +	__do_map_lock(sbi, F2FS_GET_BLOCK_PRE_AIO, false);
>>  out_sem:
>>  	up_read(&F2FS_I(inode)->i_mmap_sem);
>> -out:
>> +
>> +	f2fs_balance_fs(sbi, dn.node_changed);
>> +
>>  	sb_end_pagefault(inode->i_sb);
>>  	f2fs_update_time(sbi, REQ_TIME);
>>  err:
>> -- 
>> 2.18.0
> 
> .
>