On 25/07/16 16:35, rcochran@xxxxxxxxxxxxx wrote: > On Mon, Jul 25, 2016 at 03:56:48PM +0100, Jon Hunter wrote: >>> There is a hidden dependency between: >>> >>> - timers >>> - Block multiqueue >>> - rcutree >>> >>> If timers_dead_cpu() comes later than blk_mq_queue_reinit_notify() >>> that latter function causes a RCU stall. >> >> After this change is applied I am seeing RCU stalls during suspend >> on Tegra. I guess I am hitting the case mentioned above? How should >> this be avoided? > > The problem that I had found was a hidden dependency. When I > initially placed the timers callback into the new HP state list, that > caused a stall because the dependency was broken. The old code worked > by luck, based on the order of the notifier registrations. The new > code makes the old implicit ordering explicit, so it should work just > as well as before (famous last words). I see. >> Interestingly I am only seeing the above when using the ARM >> multi_v7_defconfig kernel configuration and not with the tegra_defconfig. >> One key difference between these is that the multi_v7_defconfig does not >> have CONFIG_PREEMPT enabled. Initial testing shows enabling CONFIG_PREEMPT >> for multi_v7_defconfig makes the problem go away. > > Just to be sure, this problem didn't exist before the HP rework, that > is, suspend worked fine with and without CONFIG_PREEMPT, right? Correct. I test suspend on Tegra with both multi_v7_defconfig (CONFIG_PREEMPT disabled) and tegra_defconfig (CONFIG_PREEMPT enabled). Looking at the git history for these configs I don't see any changes in this regard since they were added (unless some underlying Kconfig files have changed). > I see if I can find a tegra system to test with... Thanks. I have not tried another ARM based device, but I would be curious if another ARM device sees this or not. Cheers Jon -- nvpublic -- 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
