Hello, Peter. On Thu, Jan 28, 2016 at 11:12:10AM +0100, Peter Zijlstra wrote: > On Tue, Jan 26, 2016 at 06:38:43PM +0100, Thierry Reding wrote: > > > Task or work item involved in memory reclaim trying to flush a > > > non-WQ_MEM_RECLAIM workqueue or one of its work items can lead to > > > deadlock. Trigger WARN_ONCE() if such conditions are detected. > > I've started noticing the following during boot on some of the devices I > > work with: > > > > [ 4.723705] WARNING: CPU: 0 PID: 6 at kernel/workqueue.c:2361 check_flush_dependency+0x138/0x144() > > [ 4.736818] workqueue: WQ_MEM_RECLAIM deferwq:deferred_probe_work_func is flushing !WQ_MEM_RECLAIM events:lru_add_drain_per_cpu ... > Right, also, I think it makes sense to do lru_add_drain_all() from a > WQ_MEM_RECLAIM workqueue, it is, after all, aiding in getting memory > freed. > > Does something like the below cure things? > > TJ does this make sense to you? The problem here is that deferwq which has nothing to do with memory reclaim is marked with WQ_MEM_RECLAIM because it was created the old create_singlethread_workqueue() which doesn't distinguish workqueues which may be used on mem reclaim path and thus has to mark all as needing forward progress guarantee. I posted a patch to disable disable flush dependency checks on those workqueues and there's a outreachy project to weed out the users of the old interface, so hopefully this won't be an issue soon. As for whether lru drain should have WQ_MEM_RECLAIM, I'm not sure. Cc'ing linux-mm. The rule here is that any workquee which is depended upon during memory reclaim should have WQ_MEM_RECLAIM set. IOW, if a work item failing to start execution under memory pressure can prevent memory from being reclaimed, it should be scheduled on a WQ_MEM_RECLAIM workqueue. Would this be the case for lru_add_drain_per_cpu()? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
