linux-kernel - Re: 回复: 回复: [PATCH] f2fs: fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node

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Date:   Thu, 18 Jun 2020 15:31:31 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Zac <zhaowuyun@...gtech.com>, <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: 回复: 回复: [PATCH] f2fs: fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry

On 2020/6/18 11:28, Zac wrote:
>> On 2020/6/18 10:39, Zac wrote:
>>>
>>>> On 2020/6/17 17:04, zhaowuyun@...gtech.com wrote:
>>>>> From: Wuyun Zhao <zhaowuyun@...gtech.com>
>>>>>
>>>>> Under some condition, the __write_node_page will submit a page which
>> is
>>>> not
>>>>> f2fs_in_warm_node_list and will not call f2fs_add_fsync_node_entry.
>>>>> f2fs_gc continue to run to invoke f2fs_iget -> do_read_inode to read
> the
>>>> same node page
>>>>> and set code node, which make f2fs_in_warm_node_list become true,
>>>>> that will cause f2fs_bug_on in f2fs_del_fsync_node_entry when
>>>> f2fs_write_end_io called.
>>>> Could you please add below race condition description into commit
>>>> message?
>>>>
>>>> - f2fs_write_end_io
>>>> 					- f2fs_iget
>>>> 					 - do_read_inode
>>>> 					  - set_cold_node
>>>> 					  recover cold node flag
>>>>  - f2fs_in_warm_node_list
>>>>   - is_cold_node
>>>>   if node is cold, assume we have added
>>>>   node to fsync_node_list during writepages()
>>>>  - f2fs_del_fsync_node_entry
>>>>   - f2fs_bug_on() due to node page
>>>>   is not in fsync_node_list
>>>
>>> Ok, will add the commit message.
>>>
>>>> BTW, I'm curious about why we can lose cold flag for non-dir inode?
>>>> any clue to reproduce this bug (I mean losing cold flag)?
>>>
>>> it's a f2fs image with 25600MB
>>> flash this image to device
>>> the device will resize it according to the userdata partition size which
> is
>>> about 94GB
>>> the device mount the f2fs partition
>>> then hit this f2fs_bug_on
>>>
>>> seems that the cold flag is not been set when mkfs
>>
>> Ah, I guess both mkfs/sload ignores setting cold node flag for non-dir
> inode,
>> could you please send another patch to fix this issue?
> 
> Patch v2 has been sent.

I see, it looks good to me.

Actually, I meant we need to fix mkfs/sload bugs as well, do you have time to
work on it? :)

Thanks,

> 
>>>
>>> I think the issue is that
>>>
>>> 1. the node page in the storage is without cold bit
>>> 2. f2fs_disable_checkpoint -> f2fs_gc -> f2fs_get_node_page, this page
>> won't
>>> be set cold flag
>>> 3. f2fs_move_node_page -> __write_node_page to write this page
>>> 4. f2fs_gc -> f2fs_iget -> do_read_inode to read this page and set cold
> flag
>>
>> Clear enough, thanks for your explanation. :)
>>
>> Thanks,
>>
>>>
>>>>>
>>>>> [   34.966133] Call trace:
>>>>> [   34.969902]  f2fs_del_fsync_node_entry+0x100/0x108
>>>>> [   34.976071]  f2fs_write_end_io+0x1e0/0x288
>>>>> [   34.981539]  bio_endio+0x248/0x270
>>>>> [   34.986289]  blk_update_request+0x2b0/0x4d8
>>>>> [   34.991841]  scsi_end_request+0x40/0x440
>>>>> [   34.997126]  scsi_io_completion+0xa4/0x748
>>>>> [   35.002593]  scsi_finish_command+0xdc/0x110
>>>>> [   35.008143]  scsi_softirq_done+0x118/0x150
>>>>> [   35.013610]  blk_done_softirq+0x8c/0xe8
>>>>> [   35.018811]  __do_softirq+0x2e8/0x578
>>>>> [   35.023828]  irq_exit+0xfc/0x120
>>>>> [   35.028398]  handle_IPI+0x1d8/0x330
>>>>> [   35.033233]  gic_handle_irq+0x110/0x1d4
>>>>> [   35.038433]  el1_irq+0xb4/0x130
>>>>> [   35.042917]  kmem_cache_alloc+0x3f0/0x418
>>>>> [   35.048288]  radix_tree_node_alloc+0x50/0xf8
>>>>> [   35.053933]  __radix_tree_create+0xf8/0x188
>>>>> [   35.059484]  __radix_tree_insert+0x3c/0x128
>>>>> [   35.065035]  add_gc_inode+0x90/0x118
>>>>> [   35.069967]  f2fs_gc+0x1b80/0x2d70
>>>>> [   35.074718]  f2fs_disable_checkpoint+0x94/0x1d0
>>>>> [   35.080621]  f2fs_fill_super+0x10c4/0x1b88
>>>>> [   35.086088]  mount_bdev+0x194/0x1e0
>>>>> [   35.090923]  f2fs_mount+0x40/0x50
>>>>> [   35.095589]  mount_fs+0xb4/0x190
>>>>> [   35.100159]  vfs_kern_mount+0x80/0x1d8
>>>>> [   35.105260]  do_mount+0x478/0xf18
>>>>> [   35.109926]  ksys_mount+0x90/0xd0
>>>>> [   35.114592]  __arm64_sys_mount+0x24/0x38
>>>>>
>>>>> Signed-off-by: Wuyun Zhao <zhaowuyun@...gtech.com>
>>>>
>>>> Reviewed-by: Chao Yu <yuchao0@...wei.com>
>>>>
>>>> Thanks,
>>>>
>>>>> ---
>>>>>  fs/f2fs/inode.c | 1 +
>>>>>  1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>>>> index be6ac33..0df5c8c 100644
>>>>> --- a/fs/f2fs/inode.c
>>>>> +++ b/fs/f2fs/inode.c
>>>>> @@ -402,6 +402,7 @@ static int do_read_inode(struct inode *inode)
>>>>>
>>>>>  	/* try to recover cold bit for non-dir inode */
>>>>>  	if (!S_ISDIR(inode->i_mode) && !is_cold_node(node_page)) {
>>>>> +		f2fs_wait_on_page_writeback(node_page, NODE, true, true);
>>>>>  		set_cold_node(node_page, false);
>>>>>  		set_page_dirty(node_page);
>>>>>  	}
>>>>>
>>>
>>> .
>>>
> 
> .
>