No, that can't happen.
VMA changes only happen if both the mmap_sem and the page table lock is
acquired. (check insert_vm() at the end of mm/mmap.c)
The page fault path uses the map_sem, kswaps uses page_table_lock.
<< from your patch:
--- linux-2.4.2-ac20-vm/mm/vmscan.c.orig Sat Mar 17 11:30:49 2001
+++ linux-2.4.2-ac20-vm/mm/vmscan.c Sat Mar 17 20:53:10 2001
@@ -231,6 +231,7 @@
* Find the proper vm-area after freezing the vma chain
* and ptes.
*/
+ down_read(&mm->mmap_sem);
spin_lock(&mm->page_table_lock);
>>>>
Why do you acquire the mmap semaphore in swapout_mm()? The old rule was
that kswapd should never sleep on the mmap semaphore. Isn't there a
deadlock if mmap sem is already acquired? I don't remember the details.
>
> The problem is that mmap_sem seems to be protecting the list
> of VMAs, so taking _only_ the page_table_lock could let a VMA
> change under us while a page fault is underway ...
I remember that the pmd_alloc() and pte_alloc() functions need
additional locking.
--
Manfred
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