Hello, Vlastimil On Sat, Jan 16, 2016 at 09:16:41AM +0100, Vlastimil Babka wrote: > On 16.1.2016 9:06, Sergey Senozhatsky wrote: > > On (01/16/16 08:44), Vlastimil Babka wrote: > >> On 16.1.2016 5:09, Sergey Senozhatsky wrote: > >>> On (01/15/16 16:49), Vlastimil Babka wrote: > >> > >> Hmm but that's an unpin, not a pin? A mistake or I'm missing something? > > > > I'm sure it's just a compose-in-mail-app typo. > > BTW, couldn't the correct fix also just look like this? > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 9f15bdd9163c..43f743175ede 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1635,8 +1635,8 @@ static int migrate_zspage(struct zs_pool *pool, struct > size_class *class, > free_obj = obj_malloc(d_page, class, handle); > zs_object_copy(free_obj, used_obj, class); > index++; > + /* This also effectively unpins the handle */ > record_obj(handle, free_obj); > - unpin_tag(handle); > obj_free(pool, class, used_obj); > } > > But I'd still recommend WRITE_ONCE in record_obj(). And I'm not even sure it's Thanks for the reivew. Yeah, we need WRITE_ONCE in record_obj but your version will not work. IMHO, WRITE_ONCE can prevent store-tearing but it couldn't prevent reordering. IOW, we need some barrier as unlock and clear_bit_unlock includes it. So, we shouldn't omit unpin_tag there. > safe on all architectures to do a simple overwrite of a word against somebody > else trying to lock a bit there? Hmm, I think it shouldn't be a problem. It's word-alinged, word-sized store so it should be atomic. As other example, we have been used lock_page for a bit of page->flags and used other bits in there with __set_bit(ie, __SetPageXXX). I guess it's same situation with us just except we are spinning there. But it is worth to dobule check so need to help lock guys. > > > -ss > > > >> Anyway the compiler can do the same thing here without a WRITE_ONCE(). > > > > -- > > 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/ . > > Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> > > > -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>