Messages in this thread | | | From | Dan Williams <> | Date | Sat, 18 Aug 2018 22:08:53 -0700 | Subject | Re: [GIT PULL]: libnvdimm updates for v4.19-rc1 |
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/me peeks in from vacation and realizes he has left his coverage with a mess
On Sat, Aug 18, 2018 at 4:15 PM Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Fri, Aug 17, 2018 at 9:17 AM Jiang, Dave <dave.jiang@intel.com> wrote: > > > > Please pull to receive libnvdimm contributions for v4.19-rc1 > > So I don't care about the libnvdimm code itself, but when you guys add > code to the core mm/ code, I start looking. > > And when I then see shit like this: > > if (is_zone_device_page(p)) > tk->size_shift = ilog2(dev_pagemap_mapping_size(p, vma)); > > I go "No". > > There's two issues with this: > > - the damn thing can return 0, which would be an error for ilog2, and > the result is undefined > > You never check for errors. There's a check for tk->size_shift == > 0, but is that actually the guaranteed return value of ilog2(0)? No. > > - there is exactly one user of dev_pagemap_mapping_size(), and the above is it. > > Why the hell didn't that function just return the number of bits to > begin with?
In an earlier version of the patch set the raw size was used, but yes, now we only need the number of bits.
> I do not care if you screw up your own particular driver that much. > > But when I see a pull request with complete and utter garbage in the > core mm part, I will not pull. > > This is not acceptable. > > Pulled, merge conflict fixed, and then immediately unpulled again. > > I do not want to *EVER* see these kinds of patches to core MM code. > And I'm not going to pull these patches or anythinig that looks like > it has any trace of this shit. > > I get upset, because dammit, I expect better. I don't want to go "oh, > this changes core code, let's just skim over the patches" and > immediately find something fundamentally broken like this.
Yes, that's my wreckage. I particularly should have known better because I have seen your ilog2() misuse review comments on other patch sets and was careless in this instance. I was focused on the dax_lock_mapping_entry() implementation and did not circle back to sanity check this when the test case started passing (not an excuse, just thinking through how I overlooked this).
This support for turning machine checks in dax mappings into SIGBUS unfortunately ended up touching "all the things" across mm/ and x86/ in addition to drivers/nvdimm/ and drivers/dax/. It ran out of time for 4.18, and to help not miss 4.19 I offered to coordinate the series in libnvdimm.git with acks from Naoya, Ingo, and Jan.
If it can still make 4.19, would you except a fixed up branch?
The justification for pushing this sooner rather than later is to start the pipeline to the distros since enterprise in-memory-database developers reported this gap in the kernel memory error handling compared to the DRAM / page cache case.
I'm otherwise not in a position to help out on this with code until I'm back in the office mid-September, so I'd have to put this on Dave to clean up. Sorry Dave, and apologies Linus for the screw up.
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