On Thu 20-06-13 18:52:43, Satoru Takeuchi wrote: > Hi Naoya, > > At Tue, 18 Jun 2013 09:17:55 -0700, > Greg Kroah-Hartman wrote: > > > > From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > 3.9-stable review patch. If anyone has any objections, please let me know. > > > > ------------------ > > > > From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > > > > 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. I haven't checked the code closer but the patch doesn't change anything regarding pte_unmap_unlock. The only thing that it touches is the _locking_. So whether there ever was a problem with kmap or not this patch doesn't change it. That being said, the patch is OK for the stable tree. > > Thanks, > Satoru > > > > > Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> > > Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> > > Reviewed-by: Wanpeng Li <liwanp@xxxxxxxxxxxxxxxxxx> > > Reviewed-by: Michal Hocko <mhocko@xxxxxxx> > > Cc: Mel Gorman <mgorman@xxxxxxx> > > Cc: Andi Kleen <andi@xxxxxxxxxxxxxx> > > Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> > > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > > > > --- > > 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, > > > > > > -- > > To unsubscribe from this list: send the line "unsubscribe stable" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html