On Tue, May 27, 2014 at 5:01 PM, Konstantin Khlebnikov <koct9i@xxxxxxxxx> wrote: > On Tue, May 27, 2014 at 2:31 PM, Kirill A. Shutemov > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: >> Vinayak Menon wrote: >>> An issue was observed when a userspace task exits. >>> The page which hits error here is the zero page. >>> In zap_pte_range, vm_normal_page gets called, and it >>> returns a page address and not NULL, even though the >>> pte corresponds to zero pfn. In this case, >>> HAVE_PTE_SPECIAL is not set, and VM_MIXEDMAP is set >>> in vm_flags. In the case of VM_MIXEDMAP , only pfn_valid >>> is checked, and not is_zero_pfn. This results in >>> zero page being returned instead of NULL. >>> >>> BUG: Bad page map in process mediaserver pte:9dff379f pmd:9bfbd831 >>> page:c0ed8e60 count:1 mapcount:-1 mapping: (null) index:0x0 >>> page flags: 0x404(referenced|reserved) >>> addr:40c3f000 vm_flags:10220051 anon_vma: (null) mapping:d9fe0764 index:fd >>> vma->vm_ops->fault: (null) >>> vma->vm_file->f_op->mmap: binder_mmap+0x0/0x274 >> >> How do we get zero_pfn there. We shouldn't use zero page for file mappings. >> binder does some tricks? > > Its vm_ops doesn't provide ->fault method at all. > Seems like all ptes must be populated at the mmap time. > For some reason read page fault had happened and handle_pte_fault() > handled it in do_anonymous_page() which maps zero_page. > When the task crashed, it was ptraced by debuggered and the areas were dumped. And this resulted in the read page fault. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>