Messages in this thread | | | Date | Tue, 17 Jun 2008 14:20:49 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: BUG: mmapfile/writev spurious zero bytes (x86_64/not i386, bisected, reproducable) |
| |
On Tue, 17 Jun 2008, Linus Torvalds wrote: > > Hmm. Something like this *may* salvage it. > > Untested, so far (I'll reboot and test soon enough), but even if it fixes > things, it's not really very good.
Ok, so I just rebooted with this, and it does indeed fix the bug.
I'd be happier with a more complete fix (ie being byte-accurate and actually doing the partial copy when it hits a fault in the middle), but this seems to be the minimal fix, and at least fixes the totally bogus return values from the x86-64 __copy_user*() functions.
Not that I checked that I got _all_ cases correct (and maybe there are other versions of __copy_user that I missed entirely), but Bron's test-case at least seems to work properly for me now.
Bron? If you have a more complete test-suite (ie the real-world case that made you find this), it would be good to verify the whole thing.
And again, this is the kind of thing that really wants others looking at it. I personally think that this thing should likely be written as C code, with just the inner loops done as asm (ie the inner "rep movsq" and the inner 64-byte unrolled cached/uncached copies done as inline asms, and then the outer layers could be C).
Linus
| |