On Thu, Mar 31, 2016 at 5:46 PM, Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > On Thu, Mar 31, 2016 at 05:46:39PM +0900, Sergey Senozhatsky wrote: >> On (03/30/16 08:59), Minchan Kim wrote: >> > On Tue, Mar 29, 2016 at 03:02:57PM -0700, Yu Zhao wrote: >> > > zs_destroy_pool() might sleep so it shouldn't be used in zpool >> > > destroy callback which can be invoked in softirq context when >> > > zsmalloc is configured to work with zswap. >> > >> > I think it's a limitation of zswap design, not zsmalloc. >> > Could you handle it in zswap? >> >> agree. hm, looking at this backtrace >> >> > [<ffffffffaea0224b>] mutex_lock+0x1b/0x2f >> > [<ffffffffaebca4f0>] kmem_cache_destroy+0x50/0x130 >> > [<ffffffffaec10405>] zs_destroy_pool+0x85/0xe0 >> > [<ffffffffaec1046e>] zs_zpool_destroy+0xe/0x10 >> > [<ffffffffaec101a4>] zpool_destroy_pool+0x54/0x70 >> > [<ffffffffaebedac2>] __zswap_pool_release+0x62/0x90 >> > [<ffffffffaeb1037e>] rcu_process_callbacks+0x22e/0x640 >> > [<ffffffffaeb15a3e>] ? run_timer_softirq+0x3e/0x280 >> > [<ffffffffaeabe13b>] __do_softirq+0xcb/0x250 >> > [<ffffffffaeabe4dc>] irq_exit+0x9c/0xb0 >> > [<ffffffffaea03e7a>] smp_apic_timer_interrupt+0x6a/0x80 >> > [<ffffffffaf0a394f>] apic_timer_interrupt+0x7f/0x90 >> >> it also can hit the following path >> >> rcu_process_callbacks() >> __zswap_pool_release() >> zswap_pool_destroy() >> zswap_cpu_comp_destroy() >> cpu_notifier_register_begin() >> mutex_lock(&cpu_add_remove_lock); <<< >> >> can't it? >> >> -ss > > Thanks, Sergey. Now I'm convinced the problem should be fixed in > zswap. Since the rcu callback is already executed asynchronously, > using workqueue to defer the callback further more doesn't seem > to cause additional race condition at least. certainly seems appropriate to fix it in zswap, I'll work on a patch unless Seth or anyone else is already working on it. -- 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>