diff options
| -rw-r--r-- | mm/memory.c | 40 |
1 files changed, 30 insertions, 10 deletions
diff --git a/mm/memory.c b/mm/memory.c index 6ff5d729ded0..2e65df1831d9 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3029,6 +3029,17 @@ static int __do_fault(struct vm_fault *vmf) return ret; } +/* + * The ordering of these checks is important for pmds with _PAGE_DEVMAP set. + * If we check pmd_trans_unstable() first we will trip the bad_pmd() check + * inside of pmd_none_or_trans_huge_or_clear_bad(). This will end up correctly + * returning 1 but not before it spams dmesg with the pmd_clear_bad() output. + */ +static int pmd_devmap_trans_unstable(pmd_t *pmd) +{ + return pmd_devmap(*pmd) || pmd_trans_unstable(pmd); +} + static int pte_alloc_one_map(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; @@ -3052,18 +3063,27 @@ static int pte_alloc_one_map(struct vm_fault *vmf) map_pte: /* * If a huge pmd materialized under us just retry later. Use - * pmd_trans_unstable() instead of pmd_trans_huge() to ensure the pmd - * didn't become pmd_trans_huge under us and then back to pmd_none, as - * a result of MADV_DONTNEED running immediately after a huge pmd fault - * in a different thread of this mm, in turn leading to a misleading - * pmd_trans_huge() retval. All we have to ensure is that it is a - * regular pmd that we can walk with pte_offset_map() and we can do that - * through an atomic read in C, which is what pmd_trans_unstable() - * provides. + * pmd_trans_unstable() via pmd_devmap_trans_unstable() instead of + * pmd_trans_huge() to ensure the pmd didn't become pmd_trans_huge + * under us and then back to pmd_none, as a result of MADV_DONTNEED + * running immediately after a huge pmd fault in a different thread of + * this mm, in turn leading to a misleading pmd_trans_huge() retval. + * All we have to ensure is that it is a regular pmd that we can walk + * with pte_offset_map() and we can do that through an atomic read in + * C, which is what pmd_trans_unstable() provides. */ - if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd)) + if (pmd_devmap_trans_unstable(vmf->pmd)) return VM_FAULT_NOPAGE; + /* + * At this point we know that our vmf->pmd points to a page of ptes + * and it cannot become pmd_none(), pmd_devmap() or pmd_trans_huge() + * for the duration of the fault. If a racing MADV_DONTNEED runs and + * we zap the ptes pointed to by our vmf->pmd, the vmf->ptl will still + * be valid and we will re-check to make sure the vmf->pte isn't + * pte_none() under vmf->ptl protection when we return to + * alloc_set_pte(). + */ vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); return 0; @@ -3690,7 +3710,7 @@ static int handle_pte_fault(struct vm_fault *vmf) vmf->pte = NULL; } else { /* See comment in pte_alloc_one_map() */ - if (pmd_trans_unstable(vmf->pmd) || pmd_devmap(*vmf->pmd)) + if (pmd_devmap_trans_unstable(vmf->pmd)) return 0; /* * A regular pmd is established and it can't morph into a huge |