On Sat, Jul 01, 2017 at 09:40:04AM -0400, Zi Yan wrote:
> From: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
>
> If one of callers of page migration starts to handle thp,
> memory management code start to see pmd migration entry, so we need
> to prepare for it before enabling. This patch changes various code
> point which checks the status of given pmds in order to prevent race
> between thp migration and the pmd-related works.
>
> ChangeLog v1 -> v2:
> - introduce pmd_related() (I know the naming is not good, but can't
> think up no better name. Any suggesntion is welcomed.)
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
>
> ChangeLog v2 -> v3:
> - add is_swap_pmd()
> - a pmd entry should be pmd pointing to pte pages, is_swap_pmd(),
> pmd_trans_huge(), pmd_devmap(), or pmd_none()
> - pmd_none_or_trans_huge_or_clear_bad() and pmd_trans_unstable() return
> true on pmd_migration_entry, so that migration entries are not
> treated as pmd page table entries.
>
> ChangeLog v4 -> v5:
> - add explanation in pmd_none_or_trans_huge_or_clear_bad() to state
> the equivalence of !pmd_present() and is_pmd_migration_entry()
> - fix migration entry wait deadlock code (from v1) in follow_page_mask()
> - remove unnecessary code (from v1) in follow_trans_huge_pmd()
> - use is_swap_pmd() instead of !pmd_present() for pmd migration entry,
> so it will not be confused with pmd_none()
> - change author information
>
> ChangeLog v5 -> v7
> - use macro to disable the code when thp migration is not enabled
>
> ChangeLog v7 -> v8
> - remove not used code in do_huge_pmd_wp_page()
> - copy the comment from change_pte_range() on downgrading
> write migration entry to read to change_huge_pmd()
>
> Signed-off-by: Zi Yan <zi.yan@xxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> arch/x86/mm/gup.c | 7 +++--
> fs/proc/task_mmu.c | 33 ++++++++++++++-------
> include/asm-generic/pgtable.h | 17 ++++++++++-
> include/linux/huge_mm.h | 14 +++++++--
> mm/gup.c | 22 ++++++++++++--
> mm/huge_memory.c | 67 +++++++++++++++++++++++++++++++++++++++----
> mm/memcontrol.c | 5 ++++
> mm/memory.c | 12 ++++++--
> mm/mprotect.c | 4 +--
> mm/mremap.c | 2 +-
> 10 files changed, 154 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
> index 456dfdfd2249..096bbcc801e6 100644
> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -9,6 +9,7 @@
> #include <linux/vmstat.h>
> #include <linux/highmem.h>
> #include <linux/swap.h>
> +#include <linux/swapops.h>
> #include <linux/memremap.h>
>
> #include <asm/mmu_context.h>
> @@ -243,9 +244,11 @@ static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
> pmd_t pmd = *pmdp;
>
> next = pmd_addr_end(addr, end);
> - if (pmd_none(pmd))
> + if (!pmd_present(pmd)) {
> + VM_BUG_ON(is_swap_pmd(pmd) && IS_ENABLED(CONFIG_MIGRATION) &&
> + !is_pmd_migration_entry(pmd));
This VM_BUG_ON() triggers when gup is called on hugetlb hwpoison entry.
I think that in such case kernel falls into the gup slow path, and
a page fault in follow_hugetlb_page() can properly report the error to
affected processes, so no need to alarm with BUG_ON.
Could you make this VM_BUG_ON more specific, or just remove it?
Thanks,
Naoya Horiguchi
> return 0;
> - if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
> + } else if (unlikely(pmd_large(pmd))) {
> /*
> * NUMA hinting faults need to be handled in the GUP
> * slowpath for accounting purposes and so that they
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