Messages in this thread Patch in this message | | | From | "Manfred Spraul" <> | Subject | Re: changing mm->mmap_sem (was: Re: system call for process information?) | Date | Sun, 18 Mar 2001 10:34:38 +0100 |
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> > 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 ...
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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