RE: Is it possible to corrupt disk when writeback page with undetected UE?

["Luck, Tony" <tony.luck@intel.com>]

> Suppose there is a UE in a DRAM page that is backed by a disk file.
> The UE hasn't been reported to the kernel, but low level firmware
> initiated scrubbing has already logged the UE.
>
> The page is then dirtied by a write, although the write clearly failed,
> it didn't trigger an MCE.
>
> And without a subsequent read from the page, at some point, the page is
> written back to the disk, leaving a PAGE_SIZE of zeros in the targeted
> disk blocks.
>
> Is this mode of disk corruption possible?

I didn't look at what was written to disk, but I have seen this. My test sequence
was to compile and then immediately run an error injection test program that
injected a memory UC error to an instruction.

Because the program was freshly compiled, the executable file was in the
page cache with all pages marked as modified. Later a sync (or memory
pressure) wrote the dirty page with poison to filesystem.

I did see an error reported by the disk controller.

-Tony