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Date: Thu, 20 Jun 2013 18:52:43 +0900
From: Satoru Takeuchi <satoru.takeuchi@...il.com>
To: Greg Kroah-Hartman <greg@...ah.com>
Cc: linux-kernel@...r.kernel.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
Rik van Riel <riel@...hat.com>,
Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
Michal Hocko <mhocko@...e.cz>, Mel Gorman <mgorman@...e.de>,
Andi Kleen <andi@...stfloor.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [ 29/48] mm: migration: add migrate_entry_wait_huge()
Hi Naoya,
At Tue, 18 Jun 2013 09:17:55 -0700,
Greg Kroah-Hartman wrote:
>
> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> 3.9-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
>
> commit 30dad30922ccc733cfdbfe232090cf674dc374dc upstream.
>
> When we have a page fault for the address which is backed by a hugepage
> under migration, the kernel can't wait correctly and do busy looping on
> hugepage fault until the migration finishes. As a result, users who try
> to kick hugepage migration (via soft offlining, for example) occasionally
> experience long delay or soft lockup.
>
> This is because pte_offset_map_lock() can't get a correct migration entry
> or a correct page table lock for hugepage. This patch introduces
> migration_entry_wait_huge() to solve this.
I suspect that this code doesn't work correctly on i686 box with CONFIG_HIGHPTE.
If we call hugetlb_fault() -> migration_entry_wait_huge() -> __migration_entry_wait(),
this function tries to kunmap pte, in this case pte is not-kmapped pmd, via pte_unmap_unlock().
If CONFIG_DEBUG_HIGHMEM is also enabled, it results in BUG_ON() at __kunmap_atomic().
Correct me if I'm wrong.
Thanks,
Satoru
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Reviewed-by: Rik van Riel <riel@...hat.com>
> Reviewed-by: Wanpeng Li <liwanp@...ux.vnet.ibm.com>
> Reviewed-by: Michal Hocko <mhocko@...e.cz>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>
> ---
> include/linux/swapops.h | 3 +++
> mm/hugetlb.c | 2 +-
> mm/migrate.c | 23 ++++++++++++++++++-----
> 3 files changed, 22 insertions(+), 6 deletions(-)
>
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -137,6 +137,7 @@ static inline void make_migration_entry_
>
> extern void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> unsigned long address);
> +extern void migration_entry_wait_huge(struct mm_struct *mm, pte_t *pte);
> #else
>
> #define make_migration_entry(page, write) swp_entry(0, 0)
> @@ -148,6 +149,8 @@ static inline int is_migration_entry(swp
> static inline void make_migration_entry_read(swp_entry_t *entryp) { }
> static inline void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> unsigned long address) { }
> +static inline void migration_entry_wait_huge(struct mm_struct *mm,
> + pte_t *pte) { }
> static inline int is_write_migration_entry(swp_entry_t entry)
> {
> return 0;
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2823,7 +2823,7 @@ int hugetlb_fault(struct mm_struct *mm,
> if (ptep) {
> entry = huge_ptep_get(ptep);
> if (unlikely(is_hugetlb_entry_migration(entry))) {
> - migration_entry_wait(mm, (pmd_t *)ptep, address);
> + migration_entry_wait_huge(mm, ptep);
> return 0;
> } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
> return VM_FAULT_HWPOISON_LARGE |
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -200,15 +200,14 @@ static void remove_migration_ptes(struct
> * get to the page and wait until migration is finished.
> * When we return from this function the fault will be retried.
> */
> -void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> - unsigned long address)
> +static void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
> + spinlock_t *ptl)
> {
> - pte_t *ptep, pte;
> - spinlock_t *ptl;
> + pte_t pte;
> swp_entry_t entry;
> struct page *page;
>
> - ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> + spin_lock(ptl);
> pte = *ptep;
> if (!is_swap_pte(pte))
> goto out;
> @@ -236,6 +235,20 @@ out:
> pte_unmap_unlock(ptep, ptl);
> }
>
> +void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
> + unsigned long address)
> +{
> + spinlock_t *ptl = pte_lockptr(mm, pmd);
> + pte_t *ptep = pte_offset_map(pmd, address);
> + __migration_entry_wait(mm, ptep, ptl);
> +}
> +
> +void migration_entry_wait_huge(struct mm_struct *mm, pte_t *pte)
> +{
> + spinlock_t *ptl = &(mm)->page_table_lock;
> + __migration_entry_wait(mm, pte, ptl);
> +}
> +
> #ifdef CONFIG_BLOCK
> /* Returns true if all buffers are successfully locked */
> static bool buffer_migrate_lock_buffers(struct buffer_head *head,
>
>
> --
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