2014-05-01 22:09 GMT+02:00 Frederic Weisbecker <[email protected]>: > On Thu, May 01, 2014 at 03:17:20PM -0400, Don Zickus wrote: >> On Thu, May 01, 2014 at 02:55:35PM -0400, Eric Paris wrote: >> > If the CPU hits a softlockup this patch will also have it print the >> > information about all locks being held on the system. This might help >> > determine if a lock is being held too long leading to this problem. >> >> I am not sure this helps you. A softlockup is the result of pre-emption >> disabled, ie the scheduler not being called after 60 seconds. Holding a >> lock does not disable pre-emption usually. So I don't think this is going >> to add anything. >> >> Are you trying to debug a hung task? The the hung_task thread checks to >> see if a task hasn't scheduled in 2 minutes or so. That could be the >> result of long lock (but that output already dumps the lockdep stuff). > > There may be some deadlocks that lockdep doesn't detect yet. 2 example: > > 1) spinlock <-> IPI dependency > > > CPU 0 CPU 1 > -------------------------------------------------------- > spin_lock_irq(A) > smp_send_function_single_async(CPU 1, func) > //IPI > func { > spin_lock(1) > } > > But this should be resolved with a virtual lock on the IPI functions. > I should try that.
So actually this one above shouldn't be a problem because the _async version doesn't wait for the IPI to complete. But the below still looks possible. > > 2) rwlock <-> IPI > > CPU 0 CPU 1 > -------------------------------------------------------- > read_lock(A) > write_lock_irq(A) > smp_send_function_single(CPU 1, func) > //IPI never happens > > This one is much trickier. > > Anyway those are the only scenario I know of but there may be more. When > possible > we want to extend lockdep to detect new scenarios of deadlock but we don't > have the > guarantee that it can detect everything. > > So, could be useful... -- 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/
