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

> +}
> +
> 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.

thank you and regards,
o.

> __mark_inode_dirty_flag(inode, flag, false);
> }
>

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