On 03/20/2014 05:16 AM, Bob Liu wrote: > From: Vlastimil Babka <[email protected]> > > A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin fuzzing > with trinity. The call site try_to_unmap_cluster() does not lock the pages > other than its check_page parameter (which is already locked). > > The BUG_ON in mlock_vma_page() is not documented and its purpose is somewhat > unclear, but apparently it serializes against page migration, which could > otherwise fail to transfer the PG_mlocked flag. This would not be fatal, as > the > page would be eventually encountered again, but NR_MLOCK accounting would > become distorted nevertheless. This patch adds a comment to the BUG_ON in > mlock_vma_page() and munlock_vma_page() to that effect. > > The call site try_to_unmap_cluster() is fixed so that for page != check_page, > trylock_page() is attempted (to avoid possible deadlocks as we already have > check_page locked) and mlock_vma_page() is performed only upon success. If the > page lock cannot be obtained, the page is left without PG_mlocked, which is > again not a problem in the whole unevictable memory design. > > Reported-by: Sasha Levin <[email protected]> > Cc: Wanpeng Li <[email protected]> > Cc: Michel Lespinasse <[email protected]> > Cc: KOSAKI Motohiro <[email protected]> > Cc: Rik van Riel <[email protected]> > Cc: David Rientjes <[email protected]> > Cc: Mel Gorman <[email protected]> > Cc: Hugh Dickins <[email protected]> > Cc: Joonsoo Kim <[email protected]> > Cc: <[email protected]> > Signed-off-by: Vlastimil Babka <[email protected]> > Signed-off-by: Bob Liu <[email protected]>
Acked-by: Rik van Riel <[email protected]> > diff --git a/mm/mlock.c b/mm/mlock.c > index 4e1a6816..b1eb536 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -79,6 +79,7 @@ void clear_page_mlock(struct page *page) > */ > void mlock_vma_page(struct page *page) > { > + /* Serialize with page migration */ > BUG_ON(!PageLocked(page)); > > if (!TestSetPageMlocked(page)) { > @@ -174,6 +175,7 @@ unsigned int munlock_vma_page(struct page *page) > unsigned int nr_pages; > struct zone *zone = page_zone(page); > > + /* For try_to_munlock() and to serialize with page migration */ > BUG_ON(!PageLocked(page)); > > /* > diff --git a/mm/rmap.c b/mm/rmap.c > index d9d4231..43d429b 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1322,9 +1322,19 @@ static int try_to_unmap_cluster(unsigned long cursor, > unsigned int *mapcount, > BUG_ON(!page || PageAnon(page)); > > if (locked_vma) { > - mlock_vma_page(page); /* no-op if already mlocked */ > - if (page == check_page) > + if (page == check_page) { > + /* we know we have check_page locked */ > + mlock_vma_page(page); > ret = SWAP_MLOCK; > + } else if (trylock_page(page)) { > + /* > + * If we can lock the page, perform mlock. > + * Otherwise leave the page alone, it will be > + * eventually encountered again later. > + */ > + mlock_vma_page(page); > + unlock_page(page); > + } > continue; /* don't unmap */ > } > > -- All rights reversed -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
