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Groups > linux.kernel > #1210473
| From | "Kirill A. Shutemov" <kirill@shutemov.name> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCHv3 0/5] Fix compound_head() race |
| Date | 2015-08-20 14:40 +0200 |
| Message-ID | <pZxiq-4Ws-7@gated-at.bofh.it> (permalink) |
| References | <pZ7QZ-1Mc-13@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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On Wed, Aug 19, 2015 at 12:21:41PM +0300, Kirill A. Shutemov wrote:
> Here's my attempt on fixing recently discovered race in compound_head().
> It should make compound_head() reliable in all contexts.
>
> The patchset is against Linus' tree. Let me know if it need to be rebased
> onto different baseline.
>
> It's expected to have conflicts with my page-flags patchset and probably
> should be applied before it.
>
> v3:
> - Fix build without hugetlb;
> - Drop page->first_page;
> - Update comment for free_compound_page();
> - Use 'unsigned int' for page order;
>
> v2: Per Hugh's suggestion page->compound_head is moved into third double
> word. This way we can avoid memory overhead which v1 had in some
> cases.
>
> This place in struct page is rather overloaded. More testing is
> required to make sure we don't collide with anyone.
Andrew, can we have the patchset applied, if nobody has objections?
It applies cleanly into your patchstack just before my page-flags
patchset.
As expected, it causes few conflicts with patches:
page-flags-introduce-page-flags-policies-wrt-compound-pages.patch
mm-sanitize-page-mapping-for-tail-pages.patch
include-linux-page-flagsh-rename-macros-to-avoid-collisions.patch
Updated patches with solved conflicts are attached.
Let me know if I need to do anything else about this.
Hugh, does it address your worry wrt page-flags?
Before you've mentioned races of whether the head page still agrees with
the tail. I don't think it's an issue: you can get this kind of race only
in very special environments like pfn scanner where you anyway need to
re-validate the page after stabilizing it.
Bloat from my page-flags is also reduced substantially. Size of your
page_is_locked() example in allnoconfig case reduced from 32 to 17 bytes.
With the patchset it look this way:
00003070 <page_is_locked>:
3070: 8b 50 14 mov 0x14(%eax),%edx
3073: f6 c2 01 test $0x1,%dl
3076: 8d 4a ff lea -0x1(%edx),%ecx
3079: 0f 45 c1 cmovne %ecx,%eax
307c: 8b 00 mov (%eax),%eax
307e: 24 01 and $0x1,%al
3080: c3 ret
--
Kirill A. Shutemov
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[PATCHv3 0/5] Fix compound_head() race "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-08-19 11:30 +0200
[PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-08-19 11:30 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Andrew Morton <akpm@linux-foundation.org> - 2015-08-21 01:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-21 14:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Christoph Lameter <cl@linux.com> - 2015-08-21 18:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-21 21:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Andrew Morton <akpm@linux-foundation.org> - 2015-08-21 21:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Christoph Lameter <cl@linux.com> - 2015-08-21 23:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Vlastimil Babka <vbabka@suse.cz> - 2015-08-24 17:50 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Vlastimil Babka <vbabka@suse.cz> - 2015-08-25 13:50 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-25 20:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-25 22:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Vlastimil Babka <vbabka@suse.cz> - 2015-08-25 22:50 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-25 23:30 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-26 17:10 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Vlastimil Babka <vbabka@suse.cz> - 2015-08-26 17:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-26 18:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Hugh Dickins <hughd@google.com> - 2015-08-26 20:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-26 23:30 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Hugh Dickins <hughd@google.com> - 2015-08-27 00:30 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-27 01:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Michal Hocko <mhocko@kernel.org> - 2015-08-27 17:10 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Michal Hocko <mhocko@kernel.org> - 2015-08-27 18:10 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Hugh Dickins <hughd@google.com> - 2015-08-27 19:30 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Michal Hocko <mhocko@kernel.org> - 2015-08-27 20:10 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-27 18:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Michal Hocko <mhocko@kernel.org> - 2015-08-27 20:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-08-27 21:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust Jesper Dangaard Brouer <netdev@brouer.com> - 2015-08-24 02:20 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-24 11:40 +0200
Re: [PATCHv3 4/5] mm: make compound_head() robust "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-24 12:20 +0200
[PATCHv3 5/5] mm: use 'unsigned int' for page order "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2015-08-19 11:30 +0200
Re: [PATCHv3 5/5] mm: use 'unsigned int' for page order Michal Hocko <mhocko@kernel.org> - 2015-08-20 10:40 +0200
Re: [PATCHv3 0/5] Fix compound_head() race "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-20 14:40 +0200
Re: [PATCHv3 0/5] Fix compound_head() race Andrew Morton <akpm@linux-foundation.org> - 2015-08-21 01:40 +0200
Re: [PATCHv3 0/5] Fix compound_head() race Hugh Dickins <hughd@google.com> - 2015-08-22 22:20 +0200
Re: [PATCHv3 0/5] Fix compound_head() race "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-24 11:40 +0200
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