On Mon, Oct 21, 2024 at 05:34:55PM GMT, Roman Gushchin wrote: > 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.0.15 pfn:1137bb > page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff8881137bb870 pfn:0x1137bb > flags: 0x400000000080000(mlocked|node=0|zone=1) > raw: 0400000000080000 0000000000000000 dead000000000122 0000000000000000 > raw: ffff8881137bb870 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 3005, tgid > 3004 (syz.0.15), ts 61546 608067, free_ts 61390082085 > 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+0x3008/0x31f0 mm/page_alloc.c:3457 > __alloc_pages_noprof+0x292/0x7b0 mm/page_alloc.c:4733 > alloc_pages_mpol_noprof+0x3e8/0x630 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:5500 [inline] > kvm_dev_ioctl+0x13bb/0x2320 virt/kvm/kvm_main.c:5542 > vfs_ioctl fs/ioctl.c:51 [inline] > __do_sys_ioctl fs/ioctl.c:907 [inline] > __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > do_syscall_64+0x69/0x110 arch/x86/entry/common.c:83 > entry_SYSCALL_64_after_hwframe+0x76/0x7e > page last free pid 951 tgid 951 stack trace: > reset_page_owner include/linux/page_owner.h:25 [inline] > free_pages_prepare mm/page_alloc.c:1108 [inline] > free_unref_page+0xcb1/0xf00 mm/page_alloc.c:2638 > vfree+0x181/0x2e0 mm/vmalloc.c:3361 > delayed_vfree_work+0x56/0x80 mm/vmalloc.c:3282 > process_one_work kernel/workqueue.c:3229 [inline] > process_scheduled_works+0xa5c/0x17a0 kernel/workqueue.c:3310 > worker_thread+0xa2b/0xf70 kernel/workqueue.c:3391 > kthread+0x2df/0x370 kernel/kthread.c:389 > ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 > > A reproducer is available here: > https://syzkaller.appspot.com/x/repro.c?x=1437939f980000 > > The problem was originally introduced by > commit b109b87050df ("mm/munlock: replace clear_page_mlock() by final > clearance"): it was handling 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). > > Closes: https://syzkaller.appspot.com/x/report.txt?x=169a47d0580000 Can you open the access to the syzbot report?
