This patch fixes this warning by acquiring read lock before entering untrack_pfn() while write lock is not held. syzbot has tested the proposed patch and the reproducer did not trigger any issue. Reported-by: syzbot+35a4414f6e247f515443@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=35a4414f6e247f515443 Tested-by: syzbot+35a4414f6e247f515443@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Pei Li <peili.dev@xxxxxxxxx> --- Syzbot reported the following warning in follow_pte(): WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 rwsem_assert_held include/linux/rwsem.h:195 [inline] WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 mmap_assert_locked include/linux/mmap_lock.h:65 [inline] WARNING: CPU: 3 PID: 5192 at include/linux/rwsem.h:195 follow_pte+0x414/0x4c0 mm/memory.c:5980 This is because we are assuming that mm->mmap_lock should be held when entering follow_pte(). This is added in commit c5541ba378e3 (mm: follow_pte() improvements). However, in the following call stack, we are not acquring the lock: follow_phys arch/x86/mm/pat/memtype.c:957 [inline] get_pat_info+0xf2/0x510 arch/x86/mm/pat/memtype.c:991 untrack_pfn+0xf7/0x4d0 arch/x86/mm/pat/memtype.c:1104 unmap_single_vma+0x1bd/0x2b0 mm/memory.c:1819 zap_page_range_single+0x326/0x560 mm/memory.c:1920 In zap_page_range_single(), we passed mm_wr_locked as false, as we do not expect write lock to be held. In the special case where vma->vm_flags is set as VM_PFNMAP, we are hitting untrack_pfn() which eventually calls into follow_phys. This patch fixes this warning by acquiring read lock before entering untrack_pfn() while write lock is not held. syzbot has tested the proposed patch and the reproducer did not trigger any issue: Tested on: commit: 9d9a2f29 Merge tag 'mm-hotfixes-stable-2024-07-10-13-1.. git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=13be8021980000 kernel config: https://syzkaller.appspot.com/x/.config?x=3456bae478301dc8 dashboard link: https://syzkaller.appspot.com/bug?extid=35a4414f6e247f515443 compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 patch: https://syzkaller.appspot.com/x/patch.diff?x=145e3441980000 Note: testing is done by a robot and is best-effort only. --- mm/memory.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index d10e616d7389..75d7959b835b 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1815,9 +1815,16 @@ static void unmap_single_vma(struct mmu_gather *tlb, if (vma->vm_file) uprobe_munmap(vma, start, end); - if (unlikely(vma->vm_flags & VM_PFNMAP)) + if (unlikely(vma->vm_flags & VM_PFNMAP)) { + if (!mm_wr_locked) + mmap_read_lock(vma->vm_mm); + untrack_pfn(vma, 0, 0, mm_wr_locked); + if (!mm_wr_locked) + mmap_read_unlock(vma->vm_mm); + } + if (start != end) { if (unlikely(is_vm_hugetlb_page(vma))) { /* --- base-commit: 734610514cb0234763cc97ddbd235b7981889445 change-id: 20240710-bug12-fecfe4bb0dcb Best regards, -- Pei Li <peili.dev@xxxxxxxxx>
