linux-kernel - Re: 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 10:57:49 +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: [PATCH] f2fs: fix a race condition between f2fs_write_end_io and f2fs_del_fsync_node_entry

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?

> 
> 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);
>>>  	}
>>>
> 
> .
>