Re: [PATCH v9 09/14] xfs: test for always COW after the dio write checks

[sashiko-bot@kernel.org]

> A direct write to a zoned file from vectors that are not block aligned
> can silently corrupt the file's data, if the realtime flag is cleared
> and set again while the write starts.
> 
> Every bio of an always COW write has to cover whole blocks, so
> xfs_file_dio_write_aligned() passes IOMAP_DIO_FSBLOCK_ALIGNED for such
> an inode. But it tests for always COW before it takes the IOLOCK, and
> the realtime flag of a file with no blocks can change until then:
> 
>     xfs_file_dio_write_zoned()            FS_IOC_FSSETXATTR
>     ==========================            =================
>     xfs_zoned_write_space_reserve()
>                                           clears the realtime flag
>     xfs_file_dio_write_aligned()
>       xfs_is_always_cow_inode() is false
>                                           sets the realtime flag
>       xfs_ilock_iocb_for_write()
>       xfs_file_write_checks()
>       iomap_dio_rw()
>         splits a bio inside a block
> 
> The fix used here is to test for always COW once the IOLOCK is held.
> 
> Before commit 8caec6c9fef7 ("xfs: support sub-block aligned vectors in
> always COW mode"), xfs_file_dio_write() made the same test with no lock
> held, to send such vectors down the unaligned path. So v6.15 to v6.18
> have the same race, and need a different version of this fix.
> 
> Fixes: 2e2383405824 ("xfs: implement direct writes to zoned RT devices")
> Signed-off-by: Chris Mason <mason@kernel.org>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261112214604.67875-1-mason@kernel.org?part=9