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SubjectRe: [RFC][PATCH 6/8] mm: handle_speculative_fault()
On Mon, 04 Jan 2010 19:24:35 +0100
Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> Generic speculative fault handler, tries to service a pagefault
> without holding mmap_sem.
>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>


I'm sorry if I miss something...how does this patch series avoid
that vma is removed while __do_fault()->vma->vm_ops->fault() is called ?
("vma is removed" means all other things as freeing file struct etc..)

Thanks,
-Kame




> ---
> include/linux/mm.h | 2 +
> mm/memory.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 60 insertions(+), 1 deletion(-)
>
> Index: linux-2.6/mm/memory.c
> ===================================================================
> --- linux-2.6.orig/mm/memory.c
> +++ linux-2.6/mm/memory.c
> @@ -1998,7 +1998,7 @@ again:
> if (!*ptep)
> goto out;
>
> - if (vma_is_dead(vma, seq))
> + if (vma && vma_is_dead(vma, seq))
> goto unlock;
>
> unpin_page_tables();
> @@ -3112,6 +3112,63 @@ int handle_mm_fault(struct mm_struct *mm
> return handle_pte_fault(mm, vma, address, entry, pmd, flags, 0);
> }
>
> +int handle_speculative_fault(struct mm_struct *mm, unsigned long address,
> + unsigned int flags)
> +{
> + pmd_t *pmd = NULL;
> + pte_t *pte, entry;
> + spinlock_t *ptl;
> + struct vm_area_struct *vma;
> + unsigned int seq;
> + int ret = VM_FAULT_RETRY;
> + int dead;
> +
> + __set_current_state(TASK_RUNNING);
> + flags |= FAULT_FLAG_SPECULATIVE;
> +
> + count_vm_event(PGFAULT);
> +
> + rcu_read_lock();
> + if (!pte_map_lock(mm, NULL, address, pmd, flags, 0, &pte, &ptl))
> + goto out_unlock;
> +
> + vma = find_vma(mm, address);
> +
> + if (!vma)
> + goto out_unmap;
> +
> + dead = RB_EMPTY_NODE(&vma->vm_rb);
> + seq = vma->vm_sequence.sequence;
> + /*
> + * Matches both the wmb in write_seqcount_begin/end() and
> + * the wmb in detach_vmas_to_be_unmapped()/__unlink_vma().
> + */
> + smp_rmb();
> + if (dead || seq & 1)
> + goto out_unmap;
> +
> + if (!(vma->vm_end > address && vma->vm_start <= address))
> + goto out_unmap;
> +
> + if (read_seqcount_retry(&vma->vm_sequence, seq))
> + goto out_unmap;
> +
> + entry = *pte;
> +
> + pte_unmap_unlock(pte, ptl);
> +
> + ret = handle_pte_fault(mm, vma, address, entry, pmd, flags, seq);
> +
> +out_unlock:
> + rcu_read_unlock();
> + return ret;
> +
> +out_unmap:
> + pte_unmap_unlock(pte, ptl);
> + goto out_unlock;
> +}
> +
> +
> #ifndef __PAGETABLE_PUD_FOLDED
> /*
> * Allocate page upper directory.
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h
> +++ linux-2.6/include/linux/mm.h
> @@ -829,6 +829,8 @@ int invalidate_inode_page(struct page *p
> #ifdef CONFIG_MMU
> extern int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
> unsigned long address, unsigned int flags);
> +extern int handle_speculative_fault(struct mm_struct *mm,
> + unsigned long address, unsigned int flags);
> #else
> static inline int handle_mm_fault(struct mm_struct *mm,
> struct vm_area_struct *vma, unsigned long address,
>
> --
>
>



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