Messages in this thread | | | Date | Thu, 12 Apr 2007 07:52:20 +0530 | From | Srivatsa Vaddagiri <> | Subject | Re: [PATCH 7/8] Clean up workqueue.c with respect to the freezer based cpu-hotplug |
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On Tue, Apr 03, 2007 at 10:48:20PM +0530, Srivatsa Vaddagiri wrote: > > Actually, we should do this before destroy_workqueue() calls flush_workqueue(). > > Otherwise flush_cpu_workqueue() can hang forever in a similar manner. > > Yep. I guess these are a class of freezer deadlocks very similar to vfork > parent waiting on child case. I get a feeling these should become common > outside of kthread too (A waits on B for something, B gets frozen, which > means A won't freeze causing freezer to fail). Can freezer detect this > dependency somehow and thaw B automatically? Probably not that easy ..
I wonder if there is some value in "enforcing" an order in which processes get frozen i.e freeze A first before B. That may solve the deadlocks we have been discussing wrt kthread_stop and flush_workqueue as well.
The idea is similar to how deadlock wrt multiple locks are solved - where a ordering is enforced. Take Lock A first before Lock B.
If process A waits on B (like in kthread_stop or flush_workqueue), then if we:
1. Insert A and B in a list (freeze_me_first_list) 2. Have freezer scan freeze_me_first_list before the master task-list, so that it: 2a. "freezes A and waits for A to get frozen" first 2b. "freezes B and waits for B to get frozen" next
then we would avoid the nastiness of "B getting frozen first and A doesnt freeze because of that" with lesser code changes?
-- Regards, vatsa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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