Re: [PATCH v4 07/15] mm: pgtable: introduce pagetable_dtor()
From: Qi Zheng <hidden>
Date: 2025-01-06 10:56:14
Also in:
linux-arch, linux-arm-kernel, linux-m68k, linux-mips, linux-mm, linux-riscv, linux-s390, linux-sh, linux-um, lkml, loongarch, sparclinux
On 2025/1/6 18:34, Alexander Gordeev wrote:
On Mon, Dec 30, 2024 at 05:07:42PM +0800, Qi Zheng wrote:quoted
The pagetable_p*_dtor() are exactly the same except for the handling of ptlock. If we make ptlock_free() handle the case where ptdesc->ptl is NULL and remove VM_BUG_ON_PAGE() from pmd_ptlock_free(), we can unify pagetable_p*_dtor() into one function. Let's introduce pagetable_dtor() to do this. Later, pagetable_dtor() will be moved to tlb_remove_ptdesc(), so that ptlock and page table pages can be freed together (regardless of whether RCU is used). This prevents the use-after-free problem where the ptlock is freed immediately but the page table pages is freed later via RCU. Signed-off-by: Qi Zheng <redacted> Originally-by: Peter Zijlstra (Intel) [off-list ref]...quoted
diff --git a/include/linux/mm.h b/include/linux/mm.h index 5d82f42ddd5cc..cad11fa10c192 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h@@ -2992,6 +2992,15 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) { return true; } static inline void ptlock_free(struct ptdesc *ptdesc) {} #endif /* defined(CONFIG_SPLIT_PTE_PTLOCKS) */ +static inline void pagetable_dtor(struct ptdesc *ptdesc) +{ + struct folio *folio = ptdesc_folio(ptdesc); + + ptlock_free(ptdesc); + __folio_clear_pgtable(folio); + lruvec_stat_sub_folio(folio, NR_PAGETABLE); +} +If I am not mistaken, it is just pagetable_pte_dtor() rename. What is the point in moving the code around?
No, this is to unify pagetable_p*_dtor() into pagetable_dtor(), so that we can move pagetable_dtor() to __tlb_remove_table(), and then ptlock and PTE page can be freed together through RCU, which is also the main purpose of this patch series. Thanks!
quoted
static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc) { struct folio *folio = ptdesc_folio(ptdesc);@@ -3003,15 +3012,6 @@ static inline bool pagetable_pte_ctor(struct ptdesc *ptdesc) return true; } -static inline void pagetable_pte_dtor(struct ptdesc *ptdesc) -{ - struct folio *folio = ptdesc_folio(ptdesc); - - ptlock_free(ptdesc); - __folio_clear_pgtable(folio); - lruvec_stat_sub_folio(folio, NR_PAGETABLE); -} - pte_t *___pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp); static inline pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)