On Tue, Feb 28, 2012 at 09:25:02PM -0800, Hugh Dickins wrote: > We have forgotten the rules of lock nesting: the irq-safe ones must be > taken inside the non-irq-safe ones, otherwise we are open to deadlock: > > CPU0 CPU1 > ---- ---- > lock(&(&pc->lock)->rlock); > local_irq_disable(); > lock(&(&zone->lru_lock)->rlock); > lock(&(&pc->lock)->rlock); > <Interrupt> > lock(&(&zone->lru_lock)->rlock); > > To check a different locking issue, I happened to add a spin_lock to > memcg's bit_spin_lock in lock_page_cgroup(), and lockdep very quickly > complained about __mem_cgroup_commit_charge_lrucare() (on CPU1 above). > > So delete __mem_cgroup_commit_charge_lrucare(), passing a bool lrucare > to __mem_cgroup_commit_charge() instead, taking zone->lru_lock under > lock_page_cgroup() in the lrucare case. > > The original was using spin_lock_irqsave, but we'd be in more trouble > if it were ever called at interrupt time: unconditional _irq is enough. > And ClearPageLRU before del from lru, SetPageLRU before add to lru: no > strong reason, but that is the ordering used consistently elsewhere. > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx> -- 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>