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SubjectRe: [PATCH v3] f2fs: fix potential .flags overflow on 32bit architecture
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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);
>> }
>>
> .
>

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