On Wed, Jun 24, 2020 at 5:17 PM Matthew Wilcox <wi...@infradead.org> wrote: > > On Wed, Jun 24, 2020 at 04:21:24PM -0700, Dan Williams wrote: > > On Wed, Jun 24, 2020 at 5:10 AM Matthew Wilcox <wi...@infradead.org> wrote: > > > On Tue, Jun 23, 2020 at 05:01:24PM -0700, Darrick J. Wong wrote: > > > > Frankly, I've wondered why the filesystem shouldn't just be in charge of > > > > all this-- > > > > > > > > 1. kernel receives machine check > > > > 2. kernel tattles to xfs > > > > 3. xfs looks up which file(s) own the pmem range > > > > 4. xfs zeroes the region, clears the poison, and sets AS_EIO on the > > > > files > > > > > > ... machine reboots, app restarts, gets no notification anything is wrong, > > > treats zeroed region as good data, launches nuclear missiles. > > > > Isn't AS_EIO stored persistently in the file block allocation map? > > No. AS_EIO is in mapping->flags. Unless Darrick was using "sets AS_EIO" > as shorthand for something else. > > > Even if it isn't today that is included in the proposal that the > > filesystem maintains a list of poison that is coordinated with the > > pmem driver. > > I'd like to see a concrete proposal here.
There's still details to work through with respect to reflink. The latest discussion was that thread I linked about how to solve the page->index collision [1] for reverse mapping pages to files. [1]: https://lore.kernel.org/linux-ext4/20200311063942.ge10...@dread.disaster.area/ > > > > > Apps shouldn't have to do this punch-and-reallocate dance, seeing as > > > > they don't currently do that for SCSI disks and the like. > > > > > > The SCSI disk retains the error until the sector is rewritten. > > > I'm not entirely sure whether you're trying to draw an analogy with > > > error-in-page-cache or error-on-storage-medium. > > > > > > error-on-medium needs to persist until the app takes an affirmative step > > > to clear it. I presume XFS does not write zeroes to sectors with > > > errors on SCSI disks ... > > > > SCSI does not have an async mechanism to retrieve a list of poisoned > > blocks from the hardware (that I know of), pmem does. I really think > > we should not glom on pmem error handling semantics on top of the same > > infrastructure that it has handling volatile / replaceable pages. When > > Erm ... commit 6100e34b2526 has your name on it. Yes, and we're having this conversation because it turns out mm/memory-failure.c enabling for DAX is insufficient. > > > the filesystem is enabled to get involved it should impose a different > > model than generic memory error handling especially because generic > > memory-error handling has no chance to solve the reflink problem. > > > > If an application wants to survive poison consumption, signals seem > > only sufficient for interrupting an application that needs to take > > immediate action because one of its instructions was prevented from > > making forward progress. The interface for enumerating the extent of > > errors for DAX goes beyond what signinfo can reasonably convey, that > > piece is where the filesystem can be called to discover which file > > extents are impacted by poison. > > > > I like Darrick's idea that the kernel stabilizes the storage by > > default, and that the repair mechanism is just a write(2). I assume > > "stabilize" means make sure that the file offset is permanently > > recorded as poisoned until the next write(2), but read(2) and mmap(2) > > return errors so no more machine checks are triggered. > > That seems like something we'd want to work into the iomap infrastructure, > perhaps. Add an IOMAP_POISONED to indicate this range needs to be > written before it can be read? Yes, an explicit error state for an extent range is needed for the fs to offload the raw hardware poison list into software tracking. _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-le...@lists.01.org
