Re: mlockall and mmap of IO devices don't mix

[Joe Korty <joe.korty@ccur.com>]

On Fri, Oct 03, 2003 at 04:15:40PM -0700, Andrew Morton wrote:
>> Sigh.  No go; it *looks* good but my app still locks up....
> 
> Or we could use that VM_RESERVED thing?

Hi Andrew,
 Your third patch worked perfectly for all the tested cases:
    o /dev/mem at offset fd000000 (my video card mem addr)
    o /dev/mem at offset 0
    o with an mmapable device driver.

I did have to make two changes to get it to compile:

--- mm/memory.c.am3	2003-10-03 19:44:17.000000000 -0400
+++ mm/memory.c	2003-10-03 19:43:47.000000000 -0400
@@ -738,7 +738,7 @@
 #endif
 
 		special = vma->vm_flags & (VM_IO | VM_RESERVED);
-		if (!vma || (pages && vm_io) || !(flags & vma->vm_flags))
+		if (!vma || (pages && special) || !(flags & vma->vm_flags))
 			return i ? : -EFAULT;
 
 		if (is_vm_hugetlb_page(vma)) {
@@ -755,7 +755,7 @@
 			 * mappings of /dev/mem - they may have no pageframes.
 			 * And the caller passed NULL for `pages' anyway.
 			 */
-			while (!special && !(map=follow_page(mm,start,write)) {
+			while (!special && !(map=follow_page(mm,start,write))) {
 				spin_unlock(&mm->page_table_lock);
 				switch (handle_mm_fault(mm,vma,start,write)) {
 				case VM_FAULT_MINOR:

In the first change, 'special' != '(vma->vma_flags & VM_IO)' which
was what was originally being tested.  Could that cause a problem?

Also, could the use of VM_RESERVED cause in some cases memory with
pageframes to skip adjustment/use of those pageframes?

Regards, and thanks,
Joe