On Mon, Apr 17, 2023 at 09:41:41PM -0700, Hugh Dickins wrote: > On Thu, 9 Mar 2023, Luis Chamberlain wrote: > > > In theory when info->flags & VM_LOCKED we should not be getting > > shem_writepage() called so we should be verifying this with a > > WARN_ON_ONCE(). Since we should not be swapping then best to ensure > > we also don't do the folio split earlier too. So just move the check > > early to avoid folio splits in case its a dubious call. > > > > We also have a similar early bail when !total_swap_pages so just move > > that earlier to avoid the possible folio split in the same situation. > > > > Acked-by: David Hildenbrand <david@xxxxxxxxxx> > > Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx> > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > > --- > > mm/shmem.c | 10 ++++++---- > > 1 file changed, 6 insertions(+), 4 deletions(-) > > > > diff --git a/mm/shmem.c b/mm/shmem.c > > index 68e9970baf1e..dfd995da77b4 100644 > > --- a/mm/shmem.c > > +++ b/mm/shmem.c > > @@ -1350,6 +1350,12 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) > > if (WARN_ON_ONCE(!wbc->for_reclaim)) > > goto redirty; > > > > + if (WARN_ON_ONCE(info->flags & VM_LOCKED)) > > + goto redirty; > > Well, okay, I don't mind that. But shall we take bets on how soon syzbot > (hope it's not watching) will try flipping SHM_LOCK on while swapping out > pages from a SHM segment, and hit that warning? Perhaps I'm wrong, but I > don't think any serialization prevents that. I though that may be the case. Would such serialization be welcomed? Luis
