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From: Muchun Song In-Reply-To: <20240904084022.32728-11-zhengqi.arch@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT 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 > --- > 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);