Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

From	"Kirill A. Shutemov" <kirill@shutemov.name>
Newsgroups	linux.kernel
Subject	Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)
Date	2016-02-11 20:10 +0100
Message-ID	<r14MN-4Cs-9@gated-at.bofh.it> (permalink)
References	<r14a7-44q-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Feb 11, 2016 at 07:22:23PM +0100, Gerald Schaefer wrote:
> Hi,
> 
> Sebastian Ott reported random kernel crashes beginning with v4.5-rc1 and
> he also bisected this to commit 61f5d698 "mm: re-enable THP". Further
> review of the THP rework patches, which cannot be bisected, revealed
> commit fecffad "s390, thp: remove infrastructure for handling splitting PMDs"
> (and also similar commits for other archs).
> 
> This commit removes the THP splitting bit and also the architecture
> implementation of pmdp_splitting_flush(), which took care of the IPI for
> fast_gup serialization. The commit message says
> 
>     pmdp_splitting_flush() is not needed too: on splitting PMD we will do
>     pmdp_clear_flush() + set_pte_at().  pmdp_clear_flush() will do IPI as
>     needed for fast_gup
> 
> The assumption that a TLB flush will also produce an IPI is wrong on s390,
> and maybe also on other architectures, and I thought that this was actually
> the main reason for having an arch-specific pmdp_splitting_flush().
> 
> At least PowerPC and ARM also had an individual implementation of
> pmdp_splitting_flush() that used kick_all_cpus_sync() instead of a TLB
> flush to send the IPI, and those were also removed. Putting the arch
> maintainers and mailing lists on cc to verify.
> 
> On s390 this will break the IPI serialization against fast_gup, which
> would certainly explain the random kernel crashes, please revert or fix
> the pmdp_splitting_flush() removal.

Sorry for that.

I believe, the problem was already addressed for PowerPC:

http://lkml.kernel.org/g/454980831-16631-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com

I think kick_all_cpus_sync() in arch-specific pmdp_invalidate() would do
the trick, right?

If yes, I'll prepare patch tomorrow (some sleep required).

-- 
 Kirill A. Shutemov

Thread

[BUG] random kernel crashes after THP rework on s390 (maybe also on  PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-11 19:30 +0100
  Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-11 20:10 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2016-02-11 20:20 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-12 13:30 +0100
    Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-11 21:00 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-02-12 05:10 +0100
        Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-12 13:10 +0100
          Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM) "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-02-12 17:20 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Will Deacon <will.deacon@arm.com> - 2016-02-12 11:10 +0100
        Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-12 11:20 +0100
          Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Will Deacon <will.deacon@arm.com> - 2016-02-12 17:00 +0100
      Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-12 16:50 +0100
        Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Christian Borntraeger <borntraeger@de.ibm.com> - 2016-02-12 17:00 +0100
          Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-12 18:20 +0100
            Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-13 00:20 +0100
              Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-13 13:00 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-15 16:50 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-15 17:40 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-15 19:40 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-16 00:30 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-16 11:00 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-16 17:30 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-17 16:30 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Christian Borntraeger <borntraeger@de.ibm.com> - 2016-02-16 19:50 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-17 20:20 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-18 08:00 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-18 16:10 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) "Kirill A. Shutemov" <kirill@shutemov.name> - 2016-02-18 18:10 +0100
                Re: [BUG] random kernel crashes after THP rework on s390 (maybe also  on PowerPC and ARM) Sebastian Ott <sebott@linux.vnet.ibm.com> - 2016-02-19 15:20 +0100
              Re: [BUG] random kernel crashes after THP rework on s390 (maybe  also on PowerPC and ARM) Gerald Schaefer <gerald.schaefer@de.ibm.com> - 2016-02-15 17:50 +0100

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