From f57e64cada9815bd40f3c613d5cea96717c8f1af Mon Sep 17 00:00:00 2001 From: Junxiao Chang Date: Fri, 12 May 2023 15:20:36 +0800 Subject: [PATCH] mm: fix hugetlb page unmap count balance issue hugetlb page usually is mapped with pmd, but occasionally it might be mapped with pte. QEMU can use udma-buf to create host dmabufs for guest framebuffers. When QEMU is launched with parameter "hugetlb=on", udmabuffer driver maps hugetlb page with pte in page fault handler. Call chain looks like: page_add_file_rmap do_set_pte finish_fault __do_fault -> udmabuf_vm_fault, it maps hugetlb page here. do_read_fault In page_add_file_rmap(), compound is false since it is pte mapping. When qemu exits and page is unmapped in function page_remove_rmap, the hugetlb page should not be handled in pmd way. This change is to check compound parameter as well as hugetlb flag. It fixes below kernel bug which is reproduced with 6.3 kernel: [ 114.027754] BUG: Bad page cache in process qemu-system-x86 pfn:37aa00 [ 114.034288] page:000000000dd2153b refcount:514 mapcount:-4 mapping:000000004b01ca30 index:0x13800 pfn:0x37aa00 [ 114.044277] head:000000000dd2153b order:9 entire_mapcount:-4 nr_pages_mapped:4 pincount:512 [ 114.052623] aops:hugetlbfs_aops ino:6f93 [ 114.056552] flags: 0x17ffffc0010001(locked|head|node=0|zone=2|lastcpupid=0x1fffff) [ 114.064115] raw: 0017ffffc0010001 fffff7338deb0008 fffff7338dea0008 ffff98dc855ea870 [ 114.071847] raw: 000000000000009c 0000000000000002 00000202ffffffff 0000000000000000 [ 114.079572] page dumped because: still mapped when deleted [ 114.085048] CPU: 0 PID: 3122 Comm: qemu-system-x86 Tainted: G BU W E 6.3.0-v3+ #62 [ 114.093566] Hardware name: Intel Corporation Alder Lake Client Platform DDR5 SODIMM SBS RVP, BIOS ADLPFWI1.R00.3084.D89.2303211034 03/21/2023 [ 114.106839] Call Trace: [ 114.109291] [ 114.111405] dump_stack_lvl+0x4c/0x70 [ 114.115073] dump_stack+0x14/0x20 [ 114.118395] filemap_unaccount_folio+0x159/0x220 [ 114.123021] filemap_remove_folio+0x54/0x110 [ 114.127295] remove_inode_hugepages+0x111/0x5b0 [ 114.131834] hugetlbfs_evict_inode+0x23/0x50 [ 114.136111] evict+0xcd/0x1e0 [ 114.139083] iput.part.0+0x183/0x1e0 [ 114.142663] iput+0x20/0x30 [ 114.145466] dentry_unlink_inode+0xcc/0x130 [ 114.149655] __dentry_kill+0xec/0x1a0 [ 114.153325] dput+0x1ca/0x3c0 [ 114.156293] __fput+0xf4/0x280 [ 114.159357] ____fput+0x12/0x20 [ 114.162502] task_work_run+0x62/0xa0 [ 114.166088] do_exit+0x352/0xae0 [ 114.169321] do_group_exit+0x39/0x90 [ 114.172892] get_signal+0xa09/0xa30 [ 114.176391] arch_do_signal_or_restart+0x33/0x280 [ 114.181098] exit_to_user_mode_prepare+0x11f/0x190 [ 114.185893] syscall_exit_to_user_mode+0x2a/0x50 [ 114.190509] do_syscall_64+0x4c/0x90 [ 114.194095] entry_SYSCALL_64_after_hwframe+0x72/0xdc Link: https://lkml.kernel.org/r/20230512072036.1027784-1-junxiao.chang@intel.com Fixes: 53f9263baba6 ("mm: rework mapcount accounting to enable 4k mapping of THPs") Signed-off-by: Junxiao Chang Cc: Jerome Marchand Cc: Kirill A. Shutemov Cc: Michal Hocko Cc: Mike Kravetz Cc: Muchun Song Cc: James Houghton Signed-off-by: Andrew Morton --- mm/rmap.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 19392e090bec6a..b42fc0389c2437 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1377,9 +1377,9 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma, VM_BUG_ON_PAGE(compound && !PageHead(page), page); - /* Hugetlb pages are not counted in NR_*MAPPED */ - if (unlikely(folio_test_hugetlb(folio))) { - /* hugetlb pages are always mapped with pmds */ + /* Hugetlb pages usually are not counted in NR_*MAPPED */ + if (unlikely(folio_test_hugetlb(folio) && compound)) { + /* hugetlb pages are mapped with pmds */ atomic_dec(&folio->_entire_mapcount); return; }