Hi all,
I have an unexplained bug with mmap/munmap on 2.6.X.
I'm writing a kernel module that gives super-fast access to the network. It does so by doing mmap thus avoiding the memcpy to/from user.
It works well for some time but then the kernel panics with a bad_page message (full stack is given below)
What I understand from this message is that an unmapped page is being unmapped again. The bug usually appears when I unmap the area from user space.
I don't understand what I am doing wrong. I follow the example from Linux-device-driver (2nd ed.) and codes I found under drivers/.
I also saw that there's a mapping bug in the 2.6 kernels. I'm not convinced yet that this is the case, but if so, is there a work around?
relevant parts of the code are given below.
I'd appreciate any input, Hayim.
************************************88 The full panic message:
Mar 21 08:48:15 localhost kernel: Bad page state at free_hot_cold_page (in process 'noa', page c1000100) Mar 21 08:48:15 localhost kernel: flags:0x00001014 mapping:00000000 mapcount:0 count:0 Mar 21 08:48:15 localhost kernel: Backtrace: Mar 21 08:48:15 localhost kernel: [<c01329a5>] bad_page+0x75/0xb0 Mar 21 08:48:15 localhost kernel: [<c013308c>] free_hot_cold_page+0x5c/0xd0 Mar 21 08:48:15 localhost kernel: [<c013c6fb>] zap_pte_range+0x14b/0x270 Mar 21 08:48:15 localhost kernel: [<c013c873>] zap_pmd_range+0x53/0x70 Mar 21 08:48:15 localhost kernel: [<c013c8d3>] zap_pud_range+0x43/0x60 Mar 21 08:48:15 localhost kernel: [<c013c96e>] unmap_page_range+0x7e/0xa0 Mar 21 08:48:15 localhost kernel: [<c013ca81>] unmap_vmas+0xf1/0x200 Mar 21 08:48:15 localhost kernel: [<c0141005>] unmap_region+0x75/0xe0 Mar 21 08:48:15 localhost kernel: [<c0141303>] do_munmap+0x113/0x150 Mar 21 08:48:15 localhost kernel: [<c0141384>] sys_munmap+0x44/0x70 Mar 21 08:48:15 localhost kernel: [<c0102563>] syscall_call+0x7/0xb Mar 21 08:48:15 localhost kernel: Trying to fix it up, but a reboot is needed
**********************************************************8
static void sniffer_vma_open(struct vm_area_struct *vma) { printk("vma_open\n"); }
static void sniffer_vma_close(struct vm_area_struct *vma) {
printk("vma_close\n");
}static int proc_file_mmap(struct file *filp, struct vm_area_struct *vma)
{
/* don.t do anything here: "nopage" will fill the holes */
vma->vm_ops = &sniffer_vm_ops;
vma->vm_flags |= VM_RESERVED;
sniffer_vma_open(vma);
return 0;
}static struct page *proc_file_nopage(struct vm_area_struct *vma,
unsigned long address, int *type)
{
struct page *page = NOPAGE_SIGBUS;unsigned long physaddr = ((address - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
if (! page_should_be_mapped(my_page_bitmap, physaddr))
return NOPAGE_SIGBUS; page = virt_to_page((physaddr << PAGE_SHIFT));
// page = virt_to_page(__va(physaddr << PAGE_SHIFT)); // bug in LDD?
get_page(page);
return page;
}struct vm_operations_struct sniffer_vm_ops = {
.open = sniffer_vma_open,
.close = sniffer_vma_close,
.nopage = proc_file_nopage,
};
static struct file_operations File_Ops_4_Our_Proc_File = {
.read = proc_file_read,
.write = proc_file_write,
.open = proc_file_open,
.release = proc_file_close,
.mmap = proc_file_mmap,
};
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