linux-kernel - Re: [PATCH v2] f2fs: fix out-of-free problem caused by atomic write

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Date:   Fri, 3 Nov 2017 12:48:39 +0800
From:   Yunlong Song <yunlong.song@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <chao@...nel.org>, <yuchao0@...wei.com>, <yunlong.song@...oud.com>,
        <miaoxie@...wei.com>, <bintian.wang@...wei.com>,
        <linux-fsdevel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] f2fs: fix out-of-free problem caused by atomic write

Because I found that it will still lead to out-of-free problem with out 
that check.
I trace and find that it is possible that the committing date pages of 
the atomic
file is bigger than the sbi->user_block_count - valid_user_blocks(sbi), 
so I add
this check.

On 2017/11/3 11:46, Jaegeuk Kim wrote:
> On 10/30, Yunlong Song wrote:
>> f2fs_balance_fs only actives once in the commit_inmem_pages, but there
>> are more than one page to commit, so all the other pages will miss the
>> check. This will lead to out-of-free problem when commit a very large
>> file. However, we cannot do f2fs_balance_fs for each inmem page, since
>> this will break atomicity. As a result, we should collect prefree
>> segments if needed and stop atomic commit when there are not enough
>> available blocks to write atomic pages.
>>
>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
>> ---
>>   fs/f2fs/f2fs.h    |  1 +
>>   fs/f2fs/segment.c | 29 ++++++++++++++++++++++++++++-
>>   2 files changed, 29 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 13a96b8..04ce48f 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -610,6 +610,7 @@ struct f2fs_inode_info {
>>   	struct list_head inmem_pages;	/* inmemory pages managed by f2fs */
>>   	struct task_struct *inmem_task;	/* store inmemory task */
>>   	struct mutex inmem_lock;	/* lock for inmemory pages */
>> +	unsigned long inmem_blocks;	/* inmemory blocks */
>>   	struct extent_tree *extent_tree;	/* cached extent_tree entry */
>>   	struct rw_semaphore dio_rwsem[2];/* avoid racing between dio and gc */
>>   	struct rw_semaphore i_mmap_sem;
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 46dfbca..813c110 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -210,6 +210,7 @@ void register_inmem_page(struct inode *inode, struct page *page)
>>   		list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>   	inc_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
>> +	fi->inmem_blocks++;
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	trace_f2fs_register_inmem_page(page, INMEM);
>> @@ -221,6 +222,7 @@ static int __revoke_inmem_pages(struct inode *inode,
>>   	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>   	struct inmem_pages *cur, *tmp;
>>   	int err = 0;
>> +	struct f2fs_inode_info *fi = F2FS_I(inode);
>>   
>>   	list_for_each_entry_safe(cur, tmp, head, list) {
>>   		struct page *page = cur->page;
>> @@ -263,6 +265,7 @@ static int __revoke_inmem_pages(struct inode *inode,
>>   		list_del(&cur->list);
>>   		kmem_cache_free(inmem_entry_slab, cur);
>>   		dec_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
>> +		fi->inmem_blocks--;
>>   	}
>>   	return err;
>>   }
>> @@ -302,6 +305,10 @@ void drop_inmem_pages(struct inode *inode)
>>   	if (!list_empty(&fi->inmem_ilist))
>>   		list_del_init(&fi->inmem_ilist);
>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>> +	if (fi->inmem_blocks) {
>> +		f2fs_bug_on(sbi, 1);
>> +		fi->inmem_blocks = 0;
>> +	}
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	clear_inode_flag(inode, FI_ATOMIC_FILE);
>> @@ -326,6 +333,7 @@ void drop_inmem_page(struct inode *inode, struct page *page)
>>   
>>   	f2fs_bug_on(sbi, !cur || cur->page != page);
>>   	list_del(&cur->list);
>> +	fi->inmem_blocks--;
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	dec_page_count(sbi, F2FS_INMEM_PAGES);
>> @@ -410,11 +418,26 @@ int commit_inmem_pages(struct inode *inode)
>>   
>>   	INIT_LIST_HEAD(&revoke_list);
>>   	f2fs_balance_fs(sbi, true);
>> +	if (prefree_segments(sbi)
>> +		&& has_not_enough_free_secs(sbi, 0,
>> +		fi->inmem_blocks / BLKS_PER_SEC(sbi))) {
>> +		struct cp_control cpc;
>> +
>> +		cpc.reason = __get_cp_reason(sbi);
>> +		err = write_checkpoint(sbi, &cpc);
>> +		if (err)
>> +			goto drop;
>> +	}
>>   	f2fs_lock_op(sbi);
>>   
>>   	set_inode_flag(inode, FI_ATOMIC_COMMIT);
>>   
>>   	mutex_lock(&fi->inmem_lock);
>> +	if ((sbi->user_block_count - valid_user_blocks(sbi)) <
> What does this mean? We already allocated blocks successfully?
>
>> +		fi->inmem_blocks) {
>> +		err = -ENOSPC;
>> +		goto drop;
>> +	}
>>   	err = __commit_inmem_pages(inode, &revoke_list);
>>   	if (err) {
>>   		int ret;
>> @@ -429,7 +452,7 @@ int commit_inmem_pages(struct inode *inode)
>>   		ret = __revoke_inmem_pages(inode, &revoke_list, false, true);
>>   		if (ret)
>>   			err = ret;
>> -
>> +drop:
>>   		/* drop all uncommitted pages */
>>   		__revoke_inmem_pages(inode, &fi->inmem_pages, true, false);
>>   	}
>> @@ -437,6 +460,10 @@ int commit_inmem_pages(struct inode *inode)
>>   	if (!list_empty(&fi->inmem_ilist))
>>   		list_del_init(&fi->inmem_ilist);
>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>> +	if (fi->inmem_blocks) {
>> +		f2fs_bug_on(sbi, 1);
>> +		fi->inmem_blocks = 0;
>> +	}
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>> -- 
>> 1.8.5.2
> .
>

-- 
Thanks,
Yunlong Song