On 2024/9/4 16:40, Qi Zheng wrote:
In the caller of map_pte(), we may modify the pvmw->pte after acquiring the pvmw->ptl, so convert it to using pte_offset_map_rw_nolock(). At this time, the pte_same() check is not performed after the pvmw->ptl held, so we should get pmdval and do pmd_same() check to ensure the stability of pvmw->pmd. Signed-off-by: Qi Zheng <zhengqi.a...@bytedance.com> --- mm/page_vma_mapped.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index ae5cc42aa2087..f1d73fd448708 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -13,9 +13,11 @@ static inline bool not_found(struct page_vma_mapped_walk *pvmw) return false; }-static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)+static bool map_pte(struct page_vma_mapped_walk *pvmw, pmd_t *pmdvalp, + spinlock_t **ptlp) { pte_t ptent; + pmd_t pmdval;if (pvmw->flags & PVMW_SYNC) {/* Use the stricter lookup */ @@ -25,6 +27,7 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) return !!pvmw->pte; }+again:/* * It is important to return the ptl corresponding to pte, * in case *pvmw->pmd changes underneath us; so we need to @@ -32,10 +35,11 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp) * proceeds to loop over next ptes, and finds a match later. * Though, in most cases, page lock already protects this. */ - pvmw->pte = pte_offset_map_nolock(pvmw->vma->vm_mm, pvmw->pmd, - pvmw->address, ptlp); + pvmw->pte = pte_offset_map_rw_nolock(pvmw->vma->vm_mm, pvmw->pmd, + pvmw->address, &pmdval, ptlp); if (!pvmw->pte) return false; + *pmdvalp = pmdval;ptent = ptep_get(pvmw->pte); @@ -69,6 +73,12 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw, spinlock_t **ptlp)} pvmw->ptl = *ptlp; spin_lock(pvmw->ptl); + + if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pvmw->pmd)))) { + spin_unlock(pvmw->ptl);
Forgot to clear pvmw->ptl? Or how about moving the assignment for it to the place where the pmd_same check is successful?
+ goto again; + } +
Maybe here is the right place to assign pvmw->ptl. Muchun, Thanks.
return true; }@@ -278,7 +288,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)step_forward(pvmw, PMD_SIZE); continue; } - if (!map_pte(pvmw, &ptl)) { + if (!map_pte(pvmw, &pmde, &ptl)) { if (!pvmw->pte) goto restart; goto next_pte; @@ -307,6 +317,12 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) if (!pvmw->ptl) { pvmw->ptl = ptl; spin_lock(pvmw->ptl); + if (unlikely(!pmd_same(pmde, pmdp_get_lockless(pvmw->pmd)))) { + pte_unmap_unlock(pvmw->pte, pvmw->ptl); + pvmw->ptl = NULL; + pvmw->pte = NULL; + goto restart; + } } goto this_pte; } while (pvmw->address < end);
