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Tue, 30 Jul 2024 15:30:58 +0000 (GMT) X-AuditID: cbfec7f5-5acd8a8000002594-30-66a90732bea8 Received: from eusmtip1.samsung.com ( [203.254.199.221]) by eusmgms1.samsung.com (EUCPMTA) with SMTP id 4E.EA.08810.13709A66; Tue, 30 Jul 2024 16:30:57 +0100 (BST) Received: from [106.210.134.192] (unknown [106.210.134.192]) by eusmtip1.samsung.com (KnoxPortal) with ESMTPA id 20240730153057eusmtip1b3cbb5ed8e4ce8d90f540d94d16d4089~nB1gP5CrM1725417254eusmtip1n; Tue, 30 Jul 2024 15:30:57 +0000 (GMT) Message-ID: <97d87df8-6076-4df0-90a9-a8f5ddea42e9@samsung.com> Date: Tue, 30 Jul 2024 17:30:56 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm: let pte_lockptr() consume a pte_t pointer To: David Hildenbrand , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Muchun Song , Peter Xu , Oscar Salvador Content-Language: en-US From: Marek Szyprowski In-Reply-To: <20240725183955.2268884-2-david@redhat.com> Content-Transfer-Encoding: 8bit X-Brightmail-Tracker: H4sIAAAAAAAAA01SWUwTURTNmxlmBrQ4FrTXBZrU4EKkgPoxRkWMSmoiiRo/1ESxygBGFpmK ipoIahQaF2gEbEELGhWkiJRitOJCRSoIDXFBRAoxkNSARBGqAVyHqcrfufecc++5L4/GpSVe M+k9yfs5PlmdqCB9iDsNI46QRVRZXFhTvj9bVGkiWXflKM6+tBaRbJfplxd7/d57gm3O51nL o69UJKUyf9FRqmcXxwhVSUYervr08DWpqn5+RDVkDtxAbvNZHssl7jnA8aERO30S6s86sX2m FYecro9YBqoM1yJvGpglYDP+oLTIh5YypQje9bsJgZAywwharGEiMYSgXVdB/nX0DOtJkbiB YLgqF4nFIIIf95vG7RImAuy2PC8BE0wQXGttQ2J/KjTqe8c10xg5dHdcpATsx6yDwZ9ZmBbR tD8TBTlXtgozccaEwHneOK7BGRl09BoxAZNMOGgHtOOJvBkWqh6UezRyOFFTiAtmYHppKC0v QmLsNXDjWyMlYj/os1s8eDb8uicMFQynERSPdXuKHAQZrg6Pexl0OkZJIR7OLIBKa6jYXgUF jzNxoQ2ML7QPTBVD+ILuToGnLYGsU1JRPRcM9lv/1ta1vsBzkMIw4VkME840TDjH8H9vMSJu IhmXpkmK5zSLk7mDSo06SZOWHK/cnZJkRn9+0fOfdvddVNo3qLQhjEY2BDSu8JfEvLoWJ5XE qtMPc3xKDJ+WyGlsaBZNKGSSoFg5J2Xi1fu5vRy3j+P/shjtPTMDi3p29tjG1KTHy93Fp8tc b7ANJY0DgZewwuaa6BV7W68YV23Wp4yVKFc6aVnwDJ2taVeA9ajfSEhK3NO67ty+EWTxWqkn d5/J0tfq3QmqYOPAh/U7az5GjroW+qauja53oSfp/R+y++ZMTp3ST5m3dr6V68o6W61dW27v OKokskei5OmWsUiZdpJj/WZ3zPTo1MVLM782fuqus8h6jwT1aAMW3a26UKH7XnVq3pAv3xYx v7Yuf0HZ6rnm+Ha7ttA0ZOYnN4RSk9ztV9d8Lg511J+LuNzTdZB9uTHT8bTcuall9vU3adkt dEO1ulaxfYfxZHhQWIUiZNhw2y/yeHNbdYGC0CSow4NxXqP+DRjvUQW0AwAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrMIsWRmVeSWpSXmKPExsVy+t/xu7qG7CvTDM4vNbWYs34Nm8XX9b+Y LS7vmsNmcW/Nf1aLZTsfslicmVZksWX/N3YHdo9Nnyaxe5yY8ZvFY2HDVGaP9/uusnlsPl3t 8XmTXABblJ5NUX5pSapCRn5xia1StKGFkZ6hpYWekYmlnqGxeayVkamSvp1NSmpOZllqkb5d gl7Gkd67TAVrbCvuPn/D1MC43rCLkZNDQsBE4vGXmWxdjFwcQgJLGSVud59kh0jISJyc1sAK YQtL/LnWBVX0nlFi7scGRpAEr4CdxPFDU8GKWARUJZZeuAYVF5Q4OfMJC4gtKiAvcf/WDLCh wgKeEh//dTB1MXJwiAi4SUxYFAkyk1lgDaPE8eavzCA1QgKpEtebz7OB2MwC4hK3nsxnArHZ BAwlut52gcU5BSwkNu5dzQ5RYybRtbWLEcKWl2jeOpt5AqPQLCRnzEIyahaSlllIWhYwsqxi FEktLc5Nzy021CtOzC0uzUvXS87P3cQIjL1tx35u3sE479VHvUOMTByMhxglOJiVRHjjryxN E+JNSaysSi3Kjy8qzUktPsRoCgyLicxSosn5wOjPK4k3NDMwNTQxszQwtTQzVhLn9SzoSBQS SE8sSc1OTS1ILYLpY+LglGpgWhT50skk5DK/vppR8Q75fQ5cCdtKW5hEOx46sDE6108vmNZ/ t6DjZc/3veVhNvm8qy6bvInKdgk2/ikzeWGwcphUyWHmau0dPv8dVGMiTsk8uXd3rlE5z0+u a1MvqRX/2CfA9bXt2YUFd0/1+uln8+8ycgz4v+xd/L4pK2UTO95EXpXiFWO9k39Iv9D8qLnp qyx3RtG/LnaszXvmf38+zzD60QLj+zP5FFddPR/dq6ERcvdK9qpjk1J+Xnpqdju2+J5WWYI8 c8K+B/JpP9VFNa37PSdP2ebtpZ4X8fLCQtdNZ2XXvqvniUr1tn54TU2/XIUhecG09z+NFpVl dDMeXVTWKmj6qzLM4Zrg7s1KLMUZiYZazEXFiQChjpb6RgMAAA== X-CMS-MailID: 20240730153058eucas1p2319e4cc985dcdc6e98d08398c33fcfd3 X-Msg-Generator: CA Content-Type: text/plain; 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> 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