FAILED: patch "[PATCH] mm: page_alloc: move mlocked flag clearance into" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 66edc3a5894c74f8887c8af23b97593a0dd0df4d
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024111714-varsity-grub-d888@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 66edc3a5894c74f8887c8af23b97593a0dd0df4d Mon Sep 17 00:00:00 2001
From: Roman Gushchin <[email protected]>
Date: Wed, 6 Nov 2024 19:53:54 +0000
Subject: [PATCH] mm: page_alloc: move mlocked flag clearance into
free_pages_prepare()

Syzbot reported a bad page state problem caused by a page being freed using free_page() still having a mlocked flag at free_pages_prepare() stage:

  BUG: Bad page state in process syz.5.504  pfn:61f45
  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x61f45
  flags: 0xfff00000080204(referenced|workingset|mlocked|node=0|zone=1|lastcpupid=0x7ff)
  raw: 00fff00000080204 0000000000000000 dead000000000122 0000000000000000
  raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
  page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
  page_owner tracks the page as allocated
  page last allocated via order 0, migratetype Unmovable, gfp_mask 0x400dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO), pid 8443, tgid 8442 (syz.5.504), ts 201884660643, free_ts 201499827394
   set_page_owner include/linux/page_owner.h:32 [inline]
   post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1537
   prep_new_page mm/page_alloc.c:1545 [inline]
   get_page_from_freelist+0x303f/0x3190 mm/page_alloc.c:3457
   __alloc_pages_noprof+0x292/0x710 mm/page_alloc.c:4733
   alloc_pages_mpol_noprof+0x3e8/0x680 mm/mempolicy.c:2265
   kvm_coalesced_mmio_init+0x1f/0xf0 virt/kvm/coalesced_mmio.c:99
   kvm_create_vm virt/kvm/kvm_main.c:1235 [inline]
   kvm_dev_ioctl_create_vm virt/kvm/kvm_main.c:5488 [inline]
   kvm_dev_ioctl+0x12dc/0x2240 virt/kvm/kvm_main.c:5530
   __do_compat_sys_ioctl fs/ioctl.c:1007 [inline]
   __se_compat_sys_ioctl+0x510/0xc90 fs/ioctl.c:950
   do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
   __do_fast_syscall_32+0xb4/0x110 arch/x86/entry/common.c:386
   do_fast_syscall_32+0x34/0x80 arch/x86/entry/common.c:411
   entry_SYSENTER_compat_after_hwframe+0x84/0x8e
  page last free pid 8399 tgid 8399 stack trace:
   reset_page_owner include/linux/page_owner.h:25 [inline]
   free_pages_prepare mm/page_alloc.c:1108 [inline]
   free_unref_folios+0xf12/0x18d0 mm/page_alloc.c:2686
   folios_put_refs+0x76c/0x860 mm/swap.c:1007
   free_pages_and_swap_cache+0x5c8/0x690 mm/swap_state.c:335
   __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
   tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
   tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
   tlb_flush_mmu+0x3a3/0x680 mm/mmu_gather.c:373
   tlb_finish_mmu+0xd4/0x200 mm/mmu_gather.c:465
   exit_mmap+0x496/0xc40 mm/mmap.c:1926
   __mmput+0x115/0x390 kernel/fork.c:1348
   exit_mm+0x220/0x310 kernel/exit.c:571
   do_exit+0x9b2/0x28e0 kernel/exit.c:926
   do_group_exit+0x207/0x2c0 kernel/exit.c:1088
   __do_sys_exit_group kernel/exit.c:1099 [inline]
   __se_sys_exit_group kernel/exit.c:1097 [inline]
   __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1097
   x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232
   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Modules linked in:
  CPU: 0 UID: 0 PID: 8442 Comm: syz.5.504 Not tainted 6.12.0-rc6-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
  Call Trace:
   <TASK>
   __dump_stack lib/dump_stack.c:94 [inline]
   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
   bad_page+0x176/0x1d0 mm/page_alloc.c:501
   free_page_is_bad mm/page_alloc.c:918 [inline]
   free_pages_prepare mm/page_alloc.c:1100 [inline]
   free_unref_page+0xed0/0xf20 mm/page_alloc.c:2638
   kvm_destroy_vm virt/kvm/kvm_main.c:1327 [inline]
   kvm_put_kvm+0xc75/0x1350 virt/kvm/kvm_main.c:1386
   kvm_vcpu_release+0x54/0x60 virt/kvm/kvm_main.c:4143
   __fput+0x23f/0x880 fs/file_table.c:431
   task_work_run+0x24f/0x310 kernel/task_work.c:239
   exit_task_work include/linux/task_work.h:43 [inline]
   do_exit+0xa2f/0x28e0 kernel/exit.c:939
   do_group_exit+0x207/0x2c0 kernel/exit.c:1088
   __do_sys_exit_group kernel/exit.c:1099 [inline]
   __se_sys_exit_group kernel/exit.c:1097 [inline]
   __ia32_sys_exit_group+0x3f/0x40 kernel/exit.c:1097
   ia32_sys_call+0x2624/0x2630 arch/x86/include/generated/asm/syscalls_32.h:253
   do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
   __do_fast_syscall_32+0xb4/0x110 arch/x86/entry/common.c:386
   do_fast_syscall_32+0x34/0x80 arch/x86/entry/common.c:411
   entry_SYSENTER_compat_after_hwframe+0x84/0x8e
  RIP: 0023:0xf745d579
  Code: Unable to access opcode bytes at 0xf745d54f.
  RSP: 002b:00000000f75afd6c EFLAGS: 00000206 ORIG_RAX: 00000000000000fc
  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: 00000000ffffff9c RDI: 00000000f744cff4
  RBP: 00000000f717ae61 R08: 0000000000000000 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
  R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
   </TASK>

The problem was originally introduced by commit b109b87050df ("mm/munlock:
replace clear_page_mlock() by final clearance"): it was focused on handling pagecache and anonymous memory and wasn't suitable for lower level get_page()/free_page() API's used for example by KVM, as with this reproducer.

Fix it by moving the mlocked flag clearance down to free_page_prepare().

The bug itself if fairly old and harmless (aside from generating these warnings), aside from a small memory leak - "bad" pages are stopped from being allocated again.

index c6c7bb3ea71b..216fbbfbedcf 100644
@@ -1048,6 +1048,7 @@ __always_inline bool free_pages_prepare(struct page *page,
 	bool skip_kasan_poison = should_skip_kasan_poison(page);
 	bool init = want_init_on_free();
 	bool compound = PageCompound(page);
+	struct folio *folio = page_folio(page);
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
 

@@ -1057,6 +1058,20 @@ __always_inline bool free_pages_prepare(struct page *page,
 	if (memcg_kmem_online() && PageMemcgKmem(page))
 		__memcg_kmem_uncharge_page(page, order);
 
+	/*
+	 * In rare cases, when truncation or holepunching raced with
+	 * munlock after VM_LOCKED was cleared, Mlocked may still be
+	 * found set here.  This does not indicate a problem, unless
+	 * "unevictable_pgs_cleared" appears worryingly large.
+	 */
+	if (unlikely(folio_test_mlocked(folio))) {
+		long nr_pages = folio_nr_pages(folio);
+
+		__folio_clear_mlocked(folio);
+		zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages);
+		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
+	}
+
 	if (unlikely(PageHWPoison(page)) && !order) {
 		/* Do not let hwpoison pages hit pcplists/buddy */
 		reset_page_owner(page, order);

index b8e3259ea2c4..59f30a981c6f 100644
@@ -78,20 +78,6 @@ static void __page_cache_release(struct folio *folio, struct lruvec **lruvecp,
 		lruvec_del_folio(*lruvecp, folio);
 		__folio_clear_lru_flags(folio);
 	}
-
-	/*
-	 * In rare cases, when truncation or holepunching raced with
-	 * munlock after VM_LOCKED was cleared, Mlocked may still be
-	 * found set here.  This does not indicate a problem, unless
-	 * "unevictable_pgs_cleared" appears worryingly large.
-	 */
-	if (unlikely(folio_test_mlocked(folio))) {
-		long nr_pages = folio_nr_pages(folio);
-
-		__folio_clear_mlocked(folio);
-		zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages);
-		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
-	}
 }
 
 /*

For 6.6 and 6.1 please use this replacement patch:

From 9de12cbafdf2fae7d5bfdf14f4684ce3244469df Mon Sep 17 00:00:00 2001
From: Roman Gushchin <[email protected]>
Date: Wed, 6 Nov 2024 19:53:54 +0000
Subject: [PATCH] mm: page_alloc: move mlocked flag clearance into
free_pages_prepare()

commit 66edc3a5894c74f8887c8af23b97593a0dd0df4d upstream.

Syzbot reported a bad page state problem caused by a page being freed using free_page() still having a mlocked flag at free_pages_prepare() stage:

  BUG: Bad page state in process syz.5.504  pfn:61f45
  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x61f45
  flags: 0xfff00000080204(referenced|workingset|mlocked|node=0|zone=1|lastcpupid=0x7ff)
  raw: 00fff00000080204 0000000000000000 dead000000000122 0000000000000000
  raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
  page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
  page_owner tracks the page as allocated
  page last allocated via order 0, migratetype Unmovable, gfp_mask 0x400dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO), pid 8443, tgid 8442 (syz.5.504), ts 201884660643, free_ts 201499827394
   set_page_owner include/linux/page_owner.h:32 [inline]
   post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1537
   prep_new_page mm/page_alloc.c:1545 [inline]
   get_page_from_freelist+0x303f/0x3190 mm/page_alloc.c:3457
   __alloc_pages_noprof+0x292/0x710 mm/page_alloc.c:4733
   alloc_pages_mpol_noprof+0x3e8/0x680 mm/mempolicy.c:2265
   kvm_coalesced_mmio_init+0x1f/0xf0 virt/kvm/coalesced_mmio.c:99
   kvm_create_vm virt/kvm/kvm_main.c:1235 [inline]
   kvm_dev_ioctl_create_vm virt/kvm/kvm_main.c:5488 [inline]
   kvm_dev_ioctl+0x12dc/0x2240 virt/kvm/kvm_main.c:5530
   __do_compat_sys_ioctl fs/ioctl.c:1007 [inline]
   __se_compat_sys_ioctl+0x510/0xc90 fs/ioctl.c:950
   do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
   __do_fast_syscall_32+0xb4/0x110 arch/x86/entry/common.c:386
   do_fast_syscall_32+0x34/0x80 arch/x86/entry/common.c:411
   entry_SYSENTER_compat_after_hwframe+0x84/0x8e
  page last free pid 8399 tgid 8399 stack trace:
   reset_page_owner include/linux/page_owner.h:25 [inline]
   free_pages_prepare mm/page_alloc.c:1108 [inline]
   free_unref_folios+0xf12/0x18d0 mm/page_alloc.c:2686
   folios_put_refs+0x76c/0x860 mm/swap.c:1007
   free_pages_and_swap_cache+0x5c8/0x690 mm/swap_state.c:335
   __tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
   tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
   tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
   tlb_flush_mmu+0x3a3/0x680 mm/mmu_gather.c:373
   tlb_finish_mmu+0xd4/0x200 mm/mmu_gather.c:465
   exit_mmap+0x496/0xc40 mm/mmap.c:1926
   __mmput+0x115/0x390 kernel/fork.c:1348
   exit_mm+0x220/0x310 kernel/exit.c:571
   do_exit+0x9b2/0x28e0 kernel/exit.c:926
   do_group_exit+0x207/0x2c0 kernel/exit.c:1088
   __do_sys_exit_group kernel/exit.c:1099 [inline]
   __se_sys_exit_group kernel/exit.c:1097 [inline]
   __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1097
   x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232
   do_syscall_x64 arch/x86/entry/common.c:52 [inline]
   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Modules linked in:
  CPU: 0 UID: 0 PID: 8442 Comm: syz.5.504 Not tainted 6.12.0-rc6-syzkaller #0
  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
  Call Trace:
   <TASK>
   __dump_stack lib/dump_stack.c:94 [inline]
   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
   bad_page+0x176/0x1d0 mm/page_alloc.c:501
   free_page_is_bad mm/page_alloc.c:918 [inline]
   free_pages_prepare mm/page_alloc.c:1100 [inline]
   free_unref_page+0xed0/0xf20 mm/page_alloc.c:2638
   kvm_destroy_vm virt/kvm/kvm_main.c:1327 [inline]
   kvm_put_kvm+0xc75/0x1350 virt/kvm/kvm_main.c:1386
   kvm_vcpu_release+0x54/0x60 virt/kvm/kvm_main.c:4143
   __fput+0x23f/0x880 fs/file_table.c:431
   task_work_run+0x24f/0x310 kernel/task_work.c:239
   exit_task_work include/linux/task_work.h:43 [inline]
   do_exit+0xa2f/0x28e0 kernel/exit.c:939
   do_group_exit+0x207/0x2c0 kernel/exit.c:1088
   __do_sys_exit_group kernel/exit.c:1099 [inline]
   __se_sys_exit_group kernel/exit.c:1097 [inline]
   __ia32_sys_exit_group+0x3f/0x40 kernel/exit.c:1097
   ia32_sys_call+0x2624/0x2630 arch/x86/include/generated/asm/syscalls_32.h:253
   do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
   __do_fast_syscall_32+0xb4/0x110 arch/x86/entry/common.c:386
   do_fast_syscall_32+0x34/0x80 arch/x86/entry/common.c:411
   entry_SYSENTER_compat_after_hwframe+0x84/0x8e
  RIP: 0023:0xf745d579
  Code: Unable to access opcode bytes at 0xf745d54f.
  RSP: 002b:00000000f75afd6c EFLAGS: 00000206 ORIG_RAX: 00000000000000fc
  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000000000
  RDX: 0000000000000000 RSI: 00000000ffffff9c RDI: 00000000f744cff4
  RBP: 00000000f717ae61 R08: 0000000000000000 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
  R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
   </TASK>

The problem was originally introduced by commit b109b87050df ("mm/munlock:
replace clear_page_mlock() by final clearance"): it was focused on handling pagecache and anonymous memory and wasn't suitable for lower level get_page()/free_page() API's used for example by KVM, as with this reproducer.

Fix it by moving the mlocked flag clearance down to free_page_prepare().

The bug itself if fairly old and harmless (aside from generating these warnings), aside from a small memory leak - "bad" pages are stopped from being allocated again.

---
 mm/page_alloc.c | 15 +++++++++++++++
 mm/swap.c       | 20 --------------------
 2 files changed, 15 insertions(+), 20 deletions(-)

index 7272a922b838..3d7e685bdd0b 100644
@@ -1082,12 +1082,27 @@ static __always_inline bool free_pages_prepare(struct page *page,
 	int bad = 0;
 	bool skip_kasan_poison = should_skip_kasan_poison(page, fpi_flags);
 	bool init = want_init_on_free();
+	struct folio *folio = page_folio(page);
 
 	VM_BUG_ON_PAGE(PageTail(page), page);
 
 	trace_mm_page_free(page, order);
 	kmsan_free_page(page, order);
 
+	/*
+	 * In rare cases, when truncation or holepunching raced with
+	 * munlock after VM_LOCKED was cleared, Mlocked may still be
+	 * found set here.  This does not indicate a problem, unless
+	 * "unevictable_pgs_cleared" appears worryingly large.
+	 */
+	if (unlikely(folio_test_mlocked(folio))) {
+		long nr_pages = folio_nr_pages(folio);
+
+		__folio_clear_mlocked(folio);
+		zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages);
+		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
+	}
+
 	if (unlikely(PageHWPoison(page)) && !order) {
 		/*
 		 * Do not let hwpoison pages hit pcplists/buddy

index cd8f0150ba3a..42082eba42de 100644
@@ -89,14 +89,6 @@ static void __page_cache_release(struct folio *folio)
 		__folio_clear_lru_flags(folio);
 		unlock_page_lruvec_irqrestore(lruvec, flags);
 	}
-	/* See comment on folio_test_mlocked in release_pages() */
-	if (unlikely(folio_test_mlocked(folio))) {
-		long nr_pages = folio_nr_pages(folio);
-
-		__folio_clear_mlocked(folio);
-		zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages);
-		count_vm_events(UNEVICTABLE_PGCLEARED, nr_pages);
-	}
 }
 
 static void __folio_put_small(struct folio *folio)

@@ -1021,18 +1013,6 @@ void release_pages(release_pages_arg arg, int nr)
 			__folio_clear_lru_flags(folio);
 		}
 
-		/*
-		 * In rare cases, when truncation or holepunching raced with
-		 * munlock after VM_LOCKED was cleared, Mlocked may still be
-		 * found set here.  This does not indicate a problem, unless
-		 * "unevictable_pgs_cleared" appears worryingly large.
-		 */
-		if (unlikely(folio_test_mlocked(folio))) {
-			__folio_clear_mlocked(folio);
-			zone_stat_sub_folio(folio, NR_MLOCK);
-			count_vm_event(UNEVICTABLE_PGCLEARED);
-		}
-
 		list_add(&folio->lru, &pages_to_free);
 	}
 	if (lruvec)

2.47.0.338.g60cca15819-goog

I notice that there's now a 6.6.64-rc1 out for review, but without Roman's mlocked flag clearance patch. No desperate need to get it into an rc of 6.6.64, but we wouldn't want it to go missing indefinitely.

Thanks,
Hugh

Sorry for the delay, now queued up.

greg k-h