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charset="utf-8" X-RootMTR: 20240730153058eucas1p2319e4cc985dcdc6e98d08398c33fcfd3 X-EPHeader: CA CMS-TYPE: 201P X-CMS-RootMailID: 20240730153058eucas1p2319e4cc985dcdc6e98d08398c33fcfd3 References: <20240725183955.2268884-1-david@redhat.com> <20240725183955.2268884-2-david@redhat.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4D9C44000D X-Stat-Signature: zji757f7dg1q44qr574b9yq3mfnsmukk X-Rspam-User: X-HE-Tag: 1722353460-101981 X-HE-Meta: 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 6WYF+YfK pOHPDO+VmVihN9I96i2mV74syqoBo7t/6cDt97sJJZjMsWghWiRXsuTjAtBqtnBQDS61KrfAhBNtdzfDqtjjtXpWRAZxuHPf6LkPM8ly6/3EpK9VkJDkGdY7xvs6CPtEf7P/n7OHGsmDMZXqci8OV8OoFw/faLZtp6uG1mJ7B8PFKDnArlPKhxc/e8A== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25.07.2024 20:39, David Hildenbrand wrote: > pte_lockptr() is the only *_lockptr() function that doesn't consume > what would be expected: it consumes a pmd_t pointer instead of a pte_t > pointer. > > Let's change that. The two callers in pgtable-generic.c are easily > adjusted. Adjust khugepaged.c:retract_page_tables() to simply do a > pte_offset_map_nolock() to obtain the lock, even though we won't actually > be traversing the page table. > > This makes the code more similar to the other variants and avoids other > hacks to make the new pte_lockptr() version happy. pte_lockptr() users > reside now only in pgtable-generic.c. > > Maybe, using pte_offset_map_nolock() is the right thing to do because > the PTE table could have been removed in the meantime? At least it sounds > more future proof if we ever have other means of page table reclaim. > > It's not quite clear if holding the PTE table lock is really required: > what if someone else obtains the lock just after we unlock it? But we'll > leave that as is for now, maybe there are good reasons. > > This is a preparation for adapting hugetlb page table locking logic to > take the same locks as core-mm page table walkers would. > > Signed-off-by: David Hildenbrand This patch landed in today's linux-next as commit e98970a1d2d4 ("mm: let pte_lockptr() consume a pte_t pointer"). Unfortunately it causes the following issue on most of my ARM 32bit based test boards: Run /sbin/init as init process 8<--- cut here --- Unable to handle kernel NULL pointer dereference at virtual address 00000010 when read [00000010] *pgd=00000000 Internal error: Oops: 5 [#1] PREEMPT SMP ARM Modules linked in: CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.10.0-12930-ge98970a1d2d4 #15137 Hardware name: Samsung Exynos (Flattened Device Tree) PC is at __lock_acquire+0x20/0x1604 LR is at lock_acquire+0x21c/0x394 pc : []    lr : []    psr: 20000093 sp : f082dc80  ip : 00000001  fp : c1d20000 r10: 00000000  r9 : c13096c8  r8 : 00000001 r7 : 00000000  r6 : c1d20000  r5 : c1278594  r4 : c1278594 r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : 00000010 Flags: nzCv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none Control: 10c5387d  Table: 4000404a  DAC: 00000051 ... Process swapper/0 (pid: 1, stack limit = 0x(ptrval)) Stack: (0xf082dc80 to 0xf082e000) ... Call trace:  __lock_acquire from lock_acquire+0x21c/0x394  lock_acquire from _raw_spin_lock+0x3c/0x4c  _raw_spin_lock from __pte_offset_map_lock+0x64/0x118  __pte_offset_map_lock from handle_mm_fault+0xee0/0x13c8  handle_mm_fault from __get_user_pages+0x18c/0x848  __get_user_pages from get_user_pages_remote+0xdc/0x474  get_user_pages_remote from get_arg_page+0x90/0x2a4  get_arg_page from copy_string_kernel+0x14c/0x184  copy_string_kernel from kernel_execve+0x94/0x174  kernel_execve from try_to_run_init_process+0xc/0x3c  try_to_run_init_process from kernel_init+0xcc/0x12c  kernel_init from ret_from_fork+0x14/0x28 Exception stack(0xf082dfb0 to 0xf082dff8) ... ---[ end trace 0000000000000000 ]--- note: swapper/0[1] exited with irqs disabled note: swapper/0[1] exited with preempt_count 1 Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b ]--- Reverting $subject on top of next-20240730 fixes/hides this issue. > --- > include/linux/mm.h | 7 ++++--- > mm/khugepaged.c | 21 +++++++++++++++------ > mm/pgtable-generic.c | 4 ++-- > 3 files changed, 21 insertions(+), 11 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 2c6ccf088c7be..0472a5090b180 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2873,9 +2873,10 @@ static inline spinlock_t *ptlock_ptr(struct ptdesc *ptdesc) > } > #endif /* ALLOC_SPLIT_PTLOCKS */ > > -static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd) > +static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pte_t *pte) > { > - return ptlock_ptr(page_ptdesc(pmd_page(*pmd))); > + /* PTE page tables don't currently exceed a single page. */ > + return ptlock_ptr(virt_to_ptdesc(pte)); > } > > static inline bool ptlock_init(struct ptdesc *ptdesc) > @@ -2898,7 +2899,7 @@ static inline bool ptlock_init(struct ptdesc *ptdesc) > /* > * We use mm->page_table_lock to guard all pagetable pages of the mm. > */ > -static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pmd_t *pmd) > +static inline spinlock_t *pte_lockptr(struct mm_struct *mm, pte_t *pte) > { > return &mm->page_table_lock; > } > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index cdd1d8655a76b..f3b3db1046155 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -1697,12 +1697,13 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > i_mmap_lock_read(mapping); > vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) { > struct mmu_notifier_range range; > + bool retracted = false; > struct mm_struct *mm; > unsigned long addr; > pmd_t *pmd, pgt_pmd; > spinlock_t *pml; > spinlock_t *ptl; > - bool skipped_uffd = false; > + pte_t *pte; > > /* > * Check vma->anon_vma to exclude MAP_PRIVATE mappings that > @@ -1739,9 +1740,17 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > mmu_notifier_invalidate_range_start(&range); > > pml = pmd_lock(mm, pmd); > - ptl = pte_lockptr(mm, pmd); > + > + /* > + * No need to check the PTE table content, but we'll grab the > + * PTE table lock while we zap it. > + */ > + pte = pte_offset_map_nolock(mm, pmd, addr, &ptl); > + if (!pte) > + goto unlock_pmd; > if (ptl != pml) > spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); > + pte_unmap(pte); > > /* > * Huge page lock is still held, so normally the page table > @@ -1752,20 +1761,20 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff) > * repeating the anon_vma check protects from one category, > * and repeating the userfaultfd_wp() check from another. > */ > - if (unlikely(vma->anon_vma || userfaultfd_wp(vma))) { > - skipped_uffd = true; > - } else { > + if (likely(!vma->anon_vma && !userfaultfd_wp(vma))) { > pgt_pmd = pmdp_collapse_flush(vma, addr, pmd); > pmdp_get_lockless_sync(); > + retracted = true; > } > > if (ptl != pml) > spin_unlock(ptl); > +unlock_pmd: > spin_unlock(pml); > > mmu_notifier_invalidate_range_end(&range); > > - if (!skipped_uffd) { > + if (retracted) { > mm_dec_nr_ptes(mm); > page_table_check_pte_clear_range(mm, addr, pgt_pmd); > pte_free_defer(mm, pmd_pgtable(pgt_pmd)); > diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c > index a78a4adf711ac..13a7705df3f87 100644 > --- a/mm/pgtable-generic.c > +++ b/mm/pgtable-generic.c > @@ -313,7 +313,7 @@ pte_t *pte_offset_map_nolock(struct mm_struct *mm, pmd_t *pmd, > > pte = __pte_offset_map(pmd, addr, &pmdval); > if (likely(pte)) > - *ptlp = pte_lockptr(mm, &pmdval); > + *ptlp = pte_lockptr(mm, pte); > return pte; > } > > @@ -371,7 +371,7 @@ pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd, > pte = __pte_offset_map(pmd, addr, &pmdval); > if (unlikely(!pte)) > return pte; > - ptl = pte_lockptr(mm, &pmdval); > + ptl = pte_lockptr(mm, pte); > spin_lock(ptl); > if (likely(pmd_same(pmdval, pmdp_get_lockless(pmd)))) { > *ptlp = ptl; Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland