On Tue, Oct 30, 2012 at 02:04:17PM -0700, Andrew Morton wrote: > On Sat, 27 Oct 2012 19:20:46 -0200 > Cesar Eduardo Barros <cesarb@xxxxxxxxxx> wrote: > > > The block within sys_swapoff which re-inserts the swap_info into the > > swap_list in case of failure of try_to_unuse() reads a few values outside > > the swap_lock. While this is safe at that point, it is subtle code. > > > > Simplify the code by moving the reading of these values to a separate > > function, refactoring it a bit so they are read from within the > > swap_lock. This is easier to understand, and matches better the way it > > worked before I unified the insertion of the swap_info from both > > sys_swapon and sys_swapoff. > > > > This change should make no functional difference. The only real change > > is moving the read of two or three structure fields to within the lock > > (frontswap_map_get() is nothing more than a read of p->frontswap_map). > > Your patch doesn't change this, but... it is very unusual for any > subsystem's ->init method to be called under a spinlock. Because it is > highly likely that such a method will wish to do things such as memory > allocation. > > It is rare and unlikely for an ->init() method to *need* such external > locking, because all the objects it is dealing with cannot be looked up > by other threads because nothing has been registered anywhere yet. I don't believe it actually needs that locking. Dan, do you recall the details of this? > > So either frontswap is doing something wrong here or there's some > subtlety which escapes me. If the former then we should try to get > that ->init call to happen outside swap_lock. Agreed. > > And if we can do that, perhaps we can fix the regrettable GFP_ATOMIC > in zcache_new_pool(). Ouch. Yes. FYI, thanks for pulling those two patches - they looked good to me but I hadn't had a chance to test them so did not want to comment on them until that happen. Dan beat me to it and he did test them. -- 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>