On Mon, Nov 8, 2021 at 11:27 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
>
> On Fri, Nov 05, 2021 at 07:16:38PM -0600, Jane Chu wrote:
> > static size_t pmem_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
> > void *addr, size_t bytes, struct iov_iter *i, int mode)
> > {
> > + phys_addr_t pmem_off;
> > + size_t len, lead_off;
> > + struct pmem_device *pmem = dax_get_private(dax_dev);
> > + struct device *dev = pmem->bb.dev;
> > +
> > + if (unlikely(mode == DAX_OP_RECOVERY)) {
> > + lead_off = (unsigned long)addr & ~PAGE_MASK;
> > + len = PFN_PHYS(PFN_UP(lead_off + bytes));
> > + if (is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512, len)) {
> > + if (lead_off || !(PAGE_ALIGNED(bytes))) {
> > + dev_warn(dev, "Found poison, but addr(%p) and/or bytes(%#lx) not page aligned\n",
> > + addr, bytes);
> > + return (size_t) -EIO;
> > + }
> > + pmem_off = PFN_PHYS(pgoff) + pmem->data_offset;
> > + if (pmem_clear_poison(pmem, pmem_off, bytes) !=
> > + BLK_STS_OK)
> > + return (size_t) -EIO;
> > + }
> > + }
>
> This is in the wrong spot. As seen in my WIP series individual drivers
> really should not hook into copying to and from the iter, because it
> really is just one way to write to a nvdimm. How would dm-writecache
> clear the errors with this scheme?
>
> So IMHO going back to the separate recovery method as in your previous
> patch really is the way to go. If/when the 64-bit store happens we
> need to figure out a good way to clear the bad block list for that.
I think we just make error management a first class citizen of a
dax-device and stop abstracting it behind a driver callback. That way
the driver that registers the dax-device can optionally register error
management as well. Then fsdax path can do:
rc = dax_direct_access(..., &kaddr, ...);
if (unlikely(rc)) {
kaddr = dax_mk_recovery(kaddr);
dax_direct_access(..., &kaddr, ...);
return dax_recovery_{read,write}(..., kaddr, ...);
}
return copy_{mc_to_iter,from_iter_flushcache}(...);
Where, the recovery version of dax_direct_access() has the opportunity
to change the page permissions / use an alias mapping for the access,
dax_recovery_read() allows reading the good cachelines out of a
poisoned page, and dax_recovery_write() coordinates error list
management and returning a poison page to full write-back caching
operation when no more poisoned cacheline are detected in the page.
