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1d798ca3f1
Hugh has pointed that compound_head() call can be unsafe in some
context. There's one example:
CPU0 CPU1
isolate_migratepages_block()
page_count()
compound_head()
!!PageTail() == true
put_page()
tail->first_page = NULL
head = tail->first_page
alloc_pages(__GFP_COMP)
prep_compound_page()
tail->first_page = head
__SetPageTail(p);
!!PageTail() == true
<head == NULL dereferencing>
The race is pure theoretical. I don't it's possible to trigger it in
practice. But who knows.
We can fix the race by changing how encode PageTail() and compound_head()
within struct page to be able to update them in one shot.
The patch introduces page->compound_head into third double word block in
front of compound_dtor and compound_order. Bit 0 encodes PageTail() and
the rest bits are pointer to head page if bit zero is set.
The patch moves page->pmd_huge_pte out of word, just in case if an
architecture defines pgtable_t into something what can have the bit 0
set.
hugetlb_cgroup uses page->lru.next in the second tail page to store
pointer struct hugetlb_cgroup. The patch switch it to use page->private
in the second tail page instead. The space is free since ->first_page is
removed from the union.
The patch also opens possibility to remove HUGETLB_CGROUP_MIN_ORDER
limitation, since there's now space in first tail page to store struct
hugetlb_cgroup pointer. But that's out of scope of the patch.
That means page->compound_head shares storage space with:
- page->lru.next;
- page->next;
- page->rcu_head.next;
That's too long list to be absolutely sure, but looks like nobody uses
bit 0 of the word.
page->rcu_head.next guaranteed[1] to have bit 0 clean as long as we use
call_rcu(), call_rcu_bh(), call_rcu_sched(), or call_srcu(). But future
call_rcu_lazy() is not allowed as it makes use of the bit and we can
get false positive PageTail().
[1] http://lkml.kernel.org/g/20150827163634.GD4029@linux.vnet.ibm.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
124 lines
3.0 KiB
C
124 lines
3.0 KiB
C
/*
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* Copyright IBM Corporation, 2012
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* Author Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of version 2.1 of the GNU Lesser General Public License
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it would be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*
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*/
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#ifndef _LINUX_HUGETLB_CGROUP_H
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#define _LINUX_HUGETLB_CGROUP_H
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#include <linux/mmdebug.h>
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struct hugetlb_cgroup;
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/*
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* Minimum page order trackable by hugetlb cgroup.
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* At least 3 pages are necessary for all the tracking information.
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*/
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#define HUGETLB_CGROUP_MIN_ORDER 2
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#ifdef CONFIG_CGROUP_HUGETLB
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static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
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{
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VM_BUG_ON_PAGE(!PageHuge(page), page);
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if (compound_order(page) < HUGETLB_CGROUP_MIN_ORDER)
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return NULL;
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return (struct hugetlb_cgroup *)page[2].private;
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}
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static inline
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int set_hugetlb_cgroup(struct page *page, struct hugetlb_cgroup *h_cg)
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{
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VM_BUG_ON_PAGE(!PageHuge(page), page);
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if (compound_order(page) < HUGETLB_CGROUP_MIN_ORDER)
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return -1;
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page[2].private = (unsigned long)h_cg;
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return 0;
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}
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static inline bool hugetlb_cgroup_disabled(void)
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{
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return !cgroup_subsys_enabled(hugetlb_cgrp_subsys);
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}
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extern int hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
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struct hugetlb_cgroup **ptr);
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extern void hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
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struct hugetlb_cgroup *h_cg,
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struct page *page);
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extern void hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages,
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struct page *page);
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extern void hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,
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struct hugetlb_cgroup *h_cg);
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extern void hugetlb_cgroup_file_init(void) __init;
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extern void hugetlb_cgroup_migrate(struct page *oldhpage,
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struct page *newhpage);
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#else
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static inline struct hugetlb_cgroup *hugetlb_cgroup_from_page(struct page *page)
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{
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return NULL;
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}
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static inline
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int set_hugetlb_cgroup(struct page *page, struct hugetlb_cgroup *h_cg)
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{
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return 0;
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}
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static inline bool hugetlb_cgroup_disabled(void)
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{
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return true;
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}
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static inline int
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hugetlb_cgroup_charge_cgroup(int idx, unsigned long nr_pages,
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struct hugetlb_cgroup **ptr)
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{
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return 0;
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}
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static inline void
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hugetlb_cgroup_commit_charge(int idx, unsigned long nr_pages,
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struct hugetlb_cgroup *h_cg,
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struct page *page)
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{
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return;
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}
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static inline void
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hugetlb_cgroup_uncharge_page(int idx, unsigned long nr_pages, struct page *page)
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{
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return;
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}
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static inline void
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hugetlb_cgroup_uncharge_cgroup(int idx, unsigned long nr_pages,
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struct hugetlb_cgroup *h_cg)
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{
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return;
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}
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static inline void hugetlb_cgroup_file_init(void)
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{
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}
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static inline void hugetlb_cgroup_migrate(struct page *oldhpage,
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struct page *newhpage)
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{
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return;
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}
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#endif /* CONFIG_MEM_RES_CTLR_HUGETLB */
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#endif
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