What's the status of this thing? Is it stable/3.1 material? Do we have
ack/nak's for it? Anybody?
Linus
On Thu, Oct 13, 2011 at 4:16 PM, Hugh Dickins <hughd@xxxxxxxxxx> wrote:
>
> [PATCH] mm: add anon_vma locking to mremap move
>
> I don't usually pay much attention to the stale "? " addresses in
> stack backtraces, but this lucky report from Pawel Sikora hints that
> mremap's move_ptes() has inadequate locking against page migration.
>
> 3.0 BUG_ON(!PageLocked(p)) in migration_entry_to_page():
> kernel BUG at include/linux/swapops.h:105!
> RIP: 0010:[<ffffffff81127b76>] [<ffffffff81127b76>]
> migration_entry_wait+0x156/0x160
> [<ffffffff811016a1>] handle_pte_fault+0xae1/0xaf0
> [<ffffffff810feee2>] ? __pte_alloc+0x42/0x120
> [<ffffffff8112c26b>] ? do_huge_pmd_anonymous_page+0xab/0x310
> [<ffffffff81102a31>] handle_mm_fault+0x181/0x310
> [<ffffffff81106097>] ? vma_adjust+0x537/0x570
> [<ffffffff81424bed>] do_page_fault+0x11d/0x4e0
> [<ffffffff81109a05>] ? do_mremap+0x2d5/0x570
> [<ffffffff81421d5f>] page_fault+0x1f/0x30
>
> mremap's down_write of mmap_sem, together with i_mmap_mutex/lock,
> and pagetable locks, were good enough before page migration (with its
> requirement that every migration entry be found) came in; and enough
> while migration always held mmap_sem. But not enough nowadays, when
> there's memory hotremove and compaction: anon_vma lock is also needed,
> to make sure a migration entry is not dodging around behind our back.
>
> It appears that Mel's a8bef8ff6ea1 "mm: migration: avoid race between
> shift_arg_pages() and rmap_walk() during migration by not migrating
> temporary stacks" was actually a workaround for this in the special
> common case of exec's use of move_pagetables(); and we should probably
> now remove that VM_STACK_INCOMPLETE_SETUP stuff as a separate cleanup.
>
> Reported-by: Pawel Sikora <pluto@xxxxxxxx>
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
>
> mm/mremap.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> --- 3.1-rc9/mm/mremap.c 2011-07-21 19:17:23.000000000 -0700
> +++ linux/mm/mremap.c 2011-10-13 14:36:25.097780974 -0700
> @@ -77,6 +77,7 @@ static void move_ptes(struct vm_area_str
> unsigned long new_addr)
> {
> struct address_space *mapping = NULL;
> + struct anon_vma *anon_vma = vma->anon_vma;
> struct mm_struct *mm = vma->vm_mm;
> pte_t *old_pte, *new_pte, pte;
> spinlock_t *old_ptl, *new_ptl;
> @@ -95,6 +96,8 @@ static void move_ptes(struct vm_area_str
> mapping = vma->vm_file->f_mapping;
> mutex_lock(&mapping->i_mmap_mutex);
> }
> + if (anon_vma)
> + anon_vma_lock(anon_vma);
>
> /*
> * We don't have to worry about the ordering of src and dst
> @@ -121,6 +124,8 @@ static void move_ptes(struct vm_area_str
> spin_unlock(new_ptl);
> pte_unmap(new_pte - 1);
> pte_unmap_unlock(old_pte - 1, old_ptl);
> + if (anon_vma)
> + anon_vma_unlock(anon_vma);
> if (mapping)
> mutex_unlock(&mapping->i_mmap_mutex);
> mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
--
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/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href