linux-kernel - Re: [PATCH v3] f2fs: fix potential .flags overflow on 32bit architecture

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Message-ID: <1d861a2e-0045-af0c-1f5b-c45b774c83f6@huawei.com>
Date:   Mon, 23 Mar 2020 10:09:48 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Ondřej Jirman <megi@....cz>, <jaegeuk@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH v3] f2fs: fix potential .flags overflow on 32bit
 architecture

Hello Ondřej,

On 2020/3/23 9:50, Ondřej Jirman wrote:
> Hello Chao Yu,
> 
> On Mon, Mar 23, 2020 at 09:25:19AM +0800, Chao Yu wrote:
>> [snip]
>>  
>> +static inline void __set_inode_flag(struct inode *inode, int flag)
>> +{
>> +	test_and_set_bit(flag % BITS_PER_LONG,
>> +			&F2FS_I(inode)->flags[BIT_WORD(flag)]);
> 
> This can simply be:
> 
>     test_and_set_bit(flag, F2FS_I(inode)->flags);
> 
> all of these bitmap manipulation functions already will do the
> right thing to access the correct location in the flags array:
> 
>   https://elixir.bootlin.com/linux/latest/source/include/asm-generic/bitops/atomic.h#L32
> 
> see BIT_MASK and BIT_WORD use in that function.

Oops, most f2fs bitmap check uses the same form, I missed this case....

> 
>> +}
>> +
>>  static inline void set_inode_flag(struct inode *inode, int flag)
>>  {
>> -	if (!test_bit(flag, &F2FS_I(inode)->flags))
>> -		set_bit(flag, &F2FS_I(inode)->flags);
>> +	__set_inode_flag(inode, flag);
>>  	__mark_inode_dirty_flag(inode, flag, true);
>>  }
>>  
>>  static inline int is_inode_flag_set(struct inode *inode, int flag)
>>  {
>> -	return test_bit(flag, &F2FS_I(inode)->flags);
>> +	return test_bit(flag % BITS_PER_LONG,
>> +				&F2FS_I(inode)->flags[BIT_WORD(flag)]);
> 
> ditto
> 
>>  }
>>  
>>  static inline void clear_inode_flag(struct inode *inode, int flag)
>>  {
>> -	if (test_bit(flag, &F2FS_I(inode)->flags))
>> -		clear_bit(flag, &F2FS_I(inode)->flags);
>> +	test_and_clear_bit(flag % BITS_PER_LONG,
>> +				&F2FS_I(inode)->flags[BIT_WORD(flag)]);
> 
> ditto
> 
> I'm going to test the patch. It looks like that this was really
> the root cause of all those locking issues I was seeing on my
> 32-bit tablet. It seems to explain why my 64-bit systems were
> not affected, and why reverting compession fixed it too.
> Great job figuring this out.
> 
> I'll let you know soon.

Great, hoping this patch can fix the issue this time.

Thanks anyway for supporting on troubleshooting this issue.

Thanks,

> 
> thank you and regards,
> 	o.
> 
>>  	__mark_inode_dirty_flag(inode, flag, false);
>>  }
>>  
> .
>