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Date:   Fri, 3 Nov 2017 22:40:42 +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

Test:
Newest kernel source code from f2fs-dev
1G zram with f2fs
8 threads to atomic write one same file on zram
there are four kinds of atomic write at the same time:
1 no atomic start, with atomic commit
2 no atomic start, no atomic commit
3 atomic start, with atomic commit
4 atomic start, no atomic commit

And I add dump_stack after the check as following,
+       if ((sbi->user_block_count - valid_user_blocks(sbi)) <
+               fi->inmem_blocks) {
+               dump_stack();
+               err = -ENOSPC;
+               goto drop;
+       }

then we have:

[  136.237247] F2FS-fs (zram1): Unexpected flush for atomic writes: 
ino=4, npages=8193
[  136.952469] CPU: 1 PID: 1274 Comm: atomic_t2 Not tainted 4.14.0-rc4+ #109
[  136.952947] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), 
BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
[  136.953162] Call Trace:
[  136.953162]  dump_stack+0x4d/0x6e
[  136.953162]  commit_inmem_pages+0x258/0x270
[  136.953162]  ? __sb_start_write+0x48/0x80
[  136.953162]  ? __mnt_want_write_file+0x18/0x30
[  136.953162]  f2fs_ioctl+0x1025/0x1e30
[  136.953162]  ? up_write+0x25/0x30
[  136.953162]  ? f2fs_file_write_iter+0xf3/0x1e0
[  136.953162]  ? selinux_file_ioctl+0x114/0x1e0
[  136.953162]  do_vfs_ioctl+0x96/0x5a0
[  136.953162]  SyS_ioctl+0x79/0x90
[  136.953162]  ? SyS_lseek+0x87/0xb0
[  136.953162]  entry_SYSCALL_64_fastpath+0x13/0x94
[  136.953162] RIP: 0033:0x434b97
[  136.953162] RSP: 002b:00007ffc68859de8 EFLAGS: 00000202 ORIG_RAX: 
0000000000000010
[  136.953162] RAX: ffffffffffffffda RBX: 00000000006b78e0 RCX: 
0000000000434b97
[  136.953162] RDX: 00000000006b70e8 RSI: 000000000000f502 RDI: 
0000000000000003
[  136.953162] RBP: 0000000002000010 R08: 00000000006b70e8 R09: 
00000000006b7160
[  136.953162] R10: 0000000000000022 R11: 0000000000000202 R12: 
00007f491a1c4010
[  136.953162] R13: 0000000002001000 R14: 0000000002000000 R15: 
00000000006b7938

So I think we should add the check code.

On 2017/11/3 12:48, Yunlong Song wrote:
> 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


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