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 [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/