On Thu, 2016-01-28 at 12:12 -0800, Dan Williams wrote:
On Thu, Jan 28, 2016 at 10:12 AM, Toshi Kani
> Data corruption issues were observed in tests which initiated a system
> crash/reset while accessing BTT devices. This problem is reproducible.
> The BTT driver calls pmem_rw_bytes() to update data in pmem devices.
> This interface calls __copy_user_nocache(), which uses non-temporal
> stores so that the stores to pmem are persistent.
> __copy_user_nocache() uses non-temporal stores when a request size is
> 8 bytes or larger (and is aligned by 8 bytes). The BTT driver updates
> the BTT map table, which entry size is 4 bytes. Therefore, updates to
> the map table entries remain cached, and are not written to pmem after
> a crash. Since the BTT driver makes previous blocks free and uses them
> for subsequent writes, the map table ends up pointing to blocks
> allocated for other LBAs after a crash.
> Patch 1 extends __copy_user_nocache() to use non-temporal store for
> 4 byte copy. This patch fixes the BTT data corruption issue.
> Patch 2 changes arch_memcpy_to_pmem() to flush processor caches
> a request is not naturally aligned or is less than 4 bytes. This is
> defensive change.
I'm wondering if we should just document that this routine does not
support unaligned transfers? Maybe backed by a debug mode that does
the alignment check.
Yes, I agree. For this debug mode, do you have something in mind? Or
should we add a new CONFIG option like CONFIG_PMEM_DEBUG?