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Howlett" , Nico Pache , Ryan Roberts , Dev Jain Subject: [PATCH] mm: Fix the race between collapse and PT_RECLAIM under per-vma lock Date: Tue, 5 Aug 2025 11:54:47 +0800 Message-Id: <20250805035447.7958-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Barry Song The check_pmd_still_valid() call during collapse is currently only protected by the mmap_lock in write mode, which was sufficient when pt_reclaim always ran under mmap_lock in read mode. However, since madvise_dontneed can now execute under a per-VMA lock, this assumption is no longer valid. As a result, a race condition can occur between collapse and PT_RECLAIM, potentially leading to a kernel panic. [ 38.151897] Oops: general protection fault, probably for non-canonical = address 0xdffffc0000000003: 0000 [#1] SMP KASI [ 38.153519] KASAN: null-ptr-deref in range [0x0000000000000018-0x000000= 000000001f] [ 38.154605] CPU: 0 UID: 0 PID: 721 Comm: repro Not tainted 6.16.0-next-= 20250801-next-2025080 #1 PREEMPT(voluntary) [ 38.155929] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS= rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org4 [ 38.157418] RIP: 0010:kasan_byte_accessible+0x15/0x30 [ 38.158125] Code: 03 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90= 90 90 90 66 0f 1f 00 48 b8 00 00 00 00 00 fc0 [ 38.160461] RSP: 0018:ffff88800feef678 EFLAGS: 00010286 [ 38.161220] RAX: dffffc0000000000 RBX: 0000000000000001 RCX: 1ffffffff0= dde60c [ 38.162232] RDX: 0000000000000000 RSI: ffffffff85da1e18 RDI: dffffc0000= 000003 [ 38.163176] RBP: ffff88800feef698 R08: 0000000000000001 R09: 0000000000= 000000 [ 38.164195] R10: 0000000000000000 R11: ffff888016a8ba58 R12: 0000000000= 000018 [ 38.165189] R13: 0000000000000018 R14: ffffffff85da1e18 R15: 0000000000= 000000 [ 38.166100] FS: 0000000000000000(0000) GS:ffff8880e3b40000(0000) knlGS= :0000000000000000 [ 38.167137] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 38.167891] CR2: 00007f97fadfe504 CR3: 0000000007088005 CR4: 0000000000= 770ef0 [ 38.168812] PKRU: 55555554 [ 38.169275] Call Trace: [ 38.169647] [ 38.169975] ? __kasan_check_byte+0x19/0x50 [ 38.170581] lock_acquire+0xea/0x310 [ 38.171083] ? rcu_is_watching+0x19/0xc0 [ 38.171615] ? __sanitizer_cov_trace_const_cmp4+0x1a/0x20 [ 38.172343] ? __sanitizer_cov_trace_const_cmp8+0x1c/0x30 [ 38.173130] _raw_spin_lock+0x38/0x50 [ 38.173707] ? __pte_offset_map_lock+0x1a2/0x3c0 [ 38.174390] __pte_offset_map_lock+0x1a2/0x3c0 [ 38.174987] ? __pfx___pte_offset_map_lock+0x10/0x10 [ 38.175724] ? __pfx_pud_val+0x10/0x10 [ 38.176308] ? __sanitizer_cov_trace_const_cmp1+0x1e/0x30 [ 38.177183] unmap_page_range+0xb60/0x43e0 [ 38.177824] ? __pfx_unmap_page_range+0x10/0x10 [ 38.178485] ? mas_next_slot+0x133a/0x1a50 [ 38.179079] unmap_single_vma.constprop.0+0x15b/0x250 [ 38.179830] unmap_vmas+0x1fa/0x460 [ 38.180373] ? __pfx_unmap_vmas+0x10/0x10 [ 38.180994] ? __sanitizer_cov_trace_const_cmp4+0x1a/0x20 [ 38.181877] exit_mmap+0x1a2/0xb40 [ 38.182396] ? lock_release+0x14f/0x2c0 [ 38.182929] ? __pfx_exit_mmap+0x10/0x10 [ 38.183474] ? __pfx___mutex_unlock_slowpath+0x10/0x10 [ 38.184188] ? mutex_unlock+0x16/0x20 [ 38.184704] mmput+0x132/0x370 [ 38.185208] do_exit+0x7e7/0x28c0 [ 38.185682] ? __this_cpu_preempt_check+0x21/0x30 [ 38.186328] ? do_group_exit+0x1d8/0x2c0 [ 38.186873] ? __pfx_do_exit+0x10/0x10 [ 38.187401] ? __this_cpu_preempt_check+0x21/0x30 [ 38.188036] ? _raw_spin_unlock_irq+0x2c/0x60 [ 38.188634] ? lockdep_hardirqs_on+0x89/0x110 [ 38.189313] do_group_exit+0xe4/0x2c0 [ 38.189831] __x64_sys_exit_group+0x4d/0x60 [ 38.190413] x64_sys_call+0x2174/0x2180 [ 38.190935] do_syscall_64+0x6d/0x2e0 [ 38.191449] entry_SYSCALL_64_after_hwframe+0x76/0x7e This patch moves the vma_start_write() call to precede check_pmd_still_valid(), ensuring that the check is also properly protected by the per-VMA lock. Fixes: a6fde7add78d ("mm: use per_vma lock for MADV_DONTNEED") Tested-by: "Lai, Yi" Reported-by: "Lai, Yi" Closes: https://lore.kernel.org/all/aJAFrYfyzGpbm+0m@ly-workstation/ Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Qi Zheng Cc: Vlastimil Babka Cc: Jann Horn Cc: Suren Baghdasaryan Cc: Lokesh Gidra Cc: Tangquan Zheng Cc: Lance Yang Cc: Zi Yan Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Signed-off-by: Barry Song Acked-by: David Hildenbrand Acked-by: Qi Zheng Reviewed-by: Baolin Wang Reviewed-by: Lorenzo Stoakes --- mm/khugepaged.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 374a6a5193a7..6b40bdfd224c 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1172,11 +1172,11 @@ static int collapse_huge_page(struct mm_struct *mm,= unsigned long address, if (result !=3D SCAN_SUCCEED) goto out_up_write; /* check if the pmd is still valid */ + vma_start_write(vma); result =3D check_pmd_still_valid(mm, address, pmd); if (result !=3D SCAN_SUCCEED) goto out_up_write; =20 - vma_start_write(vma); anon_vma_lock_write(vma->anon_vma); =20 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address, --=20 2.39.3 (Apple Git-146)