Messages in this thread | | | Subject | Re: [RFC v5 03/11] mm: Introduce pte_spinlock for FAULT_FLAG_SPECULATIVE | From | Anshuman Khandual <> | Date | Tue, 8 Aug 2017 16:05:07 +0530 |
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On 06/16/2017 11:22 PM, Laurent Dufour wrote: > When handling page fault without holding the mmap_sem the fetch of the > pte lock pointer and the locking will have to be done while ensuring > that the VMA is not touched in our back.
It does not change things from whats happening right now, where do we check that VMA has not changed by now ?
> > So move the fetch and locking operations in a dedicated function. > > Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> > --- > mm/memory.c | 15 +++++++++++---- > 1 file changed, 11 insertions(+), 4 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 40834444ea0d..f1132f7931ef 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2240,6 +2240,13 @@ static inline void wp_page_reuse(struct vm_fault *vmf) > pte_unmap_unlock(vmf->pte, vmf->ptl); > } > > +static bool pte_spinlock(struct vm_fault *vmf) > +{ > + vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > + spin_lock(vmf->ptl); > + return true; > +} > +
Moving them together makes sense but again if blocks are redundant when it returns true all the time.
> static bool pte_map_lock(struct vm_fault *vmf) > { > vmf->pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); > @@ -3552,8 +3559,8 @@ static int do_numa_page(struct vm_fault *vmf) > * validation through pte_unmap_same(). It's of NUMA type but > * the pfn may be screwed if the read is non atomic. > */ > - vmf->ptl = pte_lockptr(vma->vm_mm, vmf->pmd); > - spin_lock(vmf->ptl); > + if (!pte_spinlock(vmf)) > + return VM_FAULT_RETRY; > if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) { > pte_unmap_unlock(vmf->pte, vmf->ptl); > goto out; > @@ -3745,8 +3752,8 @@ static int handle_pte_fault(struct vm_fault *vmf) > if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma)) > return do_numa_page(vmf); > > - vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); > - spin_lock(vmf->ptl); > + if (!pte_spinlock(vmf)) > + return VM_FAULT_RETRY; > entry = vmf->orig_pte; > if (unlikely(!pte_same(*vmf->pte, entry))) > goto unlock; >
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