| Message ID | 20141024.133249.71272218161411159.davem@davemloft.net |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
On Fri, Oct 24, 2014 at 10:32 AM, David Miller <davem@davemloft.net> wrote: > > It's really idiotic to have a weak symbolled fallback that just > returns zero, and causes this kind of bug. There should be no > backup implementation and the link should fail if the architecture > fails to provide __get_user_pages_fast() and supports transparent > hugepages. Agreed. I think the weak fallback is for the "no hugepages support" case, but that does sound very annoying and fragile. Linus -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 24 Oct 2014 12:47:48 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote: > On Fri, Oct 24, 2014 at 10:32 AM, David Miller <davem@davemloft.net> wrote: > > > > It's really idiotic to have a weak symbolled fallback that just > > returns zero, and causes this kind of bug. There should be no > > backup implementation and the link should fail if the architecture > > fails to provide __get_user_pages_fast() and supports transparent > > hugepages. > > Agreed. I think the weak fallback is for the "no hugepages support" > case, but that does sound very annoying and fragile. > Yup. I'm thinking the get_user_pages_fast() and __get_user_pages_fast() in mm/util.c should be made non-weak and moved to mm/nommu.c. With that change, MMU architctures will need to either define CONFIG_HAVE_GENERIC_RCU_GUP or implement their own versions. Perhaps sparc should be defining CONFIG_HAVE_GENERIC_RCU_GUP. We really should switch x86 to the generic version - from a quick read it looks like it will work without needing any changes. Steve, thoughts? -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Andrew Morton <akpm@linux-foundation.org> Date: Mon, 27 Oct 2014 14:09:38 -0700 > Perhaps sparc should be defining CONFIG_HAVE_GENERIC_RCU_GUP. > > We really should switch x86 to the generic version - from a quick read > it looks like it will work without needing any changes. > > Steve, thoughts? We need to add the necessary hooks to the generic code so that x86 doesn't so specualtive gets and instead do direct increments, otherwise it's a performance regression, and then sparc can make use of that as well. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Oct 27, 2014 at 06:43:27PM -0400, David Miller wrote: > From: Andrew Morton <akpm@linux-foundation.org> > Date: Mon, 27 Oct 2014 14:09:38 -0700 > > > Perhaps sparc should be defining CONFIG_HAVE_GENERIC_RCU_GUP. > > > > We really should switch x86 to the generic version - from a quick read > > it looks like it will work without needing any changes. > > > > Steve, thoughts? > > We need to add the necessary hooks to the generic code so that x86 > doesn't so specualtive gets and instead do direct increments, > otherwise it's a performance regression, and then sparc can make use > of that as well. Agreed, I think x86 may require a helper to read 64-bit ptes (as it can't do that atomically). Also I think there's some subtlety in the way access_ok works that should be checked. The overall structure of the code looks the same to me, and I think it would be beneficial to extend then use the generic version for x86. Cheers,
Please pull to get these two bug fixes: 1) Fix boots with gcc-4.9 compiled sparc64 kernels. 2) Add missing __get_user_pages_fast() on sparc64 to fix hangs on futexes used in transparent hugepage areas. It's really idiotic to have a weak symbolled fallback that just returns zero, and causes this kind of bug. There should be no backup implementation and the link should fail if the architecture fails to provide __get_user_pages_fast() and supports transparent hugepages. Thanks. The following changes since commit 61ed53deb1c6a4386d8710dbbfcee8779c381931: Merge tag 'ntb-3.18' of git://github.com/jonmason/ntb (2014-10-19 12:58:22 -0700) are available in the git repository at: git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc.git master for you to fetch changes up to 06090e8ed89ea2113a236befb41f71d51f100e60: sparc64: Implement __get_user_pages_fast(). (2014-10-24 09:59:02 -0700) ---------------------------------------------------------------- David S. Miller (2): sparc64: Fix register corruption in top-most kernel stack frame during boot. sparc64: Implement __get_user_pages_fast(). arch/sparc/include/asm/oplib_64.h | 3 ++- arch/sparc/include/asm/setup.h | 2 ++ arch/sparc/kernel/entry.h | 3 --- arch/sparc/kernel/head_64.S | 40 ++++------------------------------------ arch/sparc/kernel/hvtramp.S | 1 - arch/sparc/kernel/setup_64.c | 28 ++++++++++++++++++++-------- arch/sparc/kernel/trampoline_64.S | 12 +++++++----- arch/sparc/mm/gup.c | 30 ++++++++++++++++++++++++++++++ arch/sparc/prom/cif.S | 5 ++--- arch/sparc/prom/init_64.c | 6 +++--- arch/sparc/prom/p1275.c | 2 -- 11 files changed, 70 insertions(+), 62 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html