On 11/21/2017 01:31 PM, Christian Borntraeger wrote: > > > On 11/21/2017 09:21 PM, Jens Axboe wrote: >> On 11/21/2017 01:19 PM, Christian Borntraeger wrote: >>> >>> On 11/21/2017 09:14 PM, Jens Axboe wrote: >>>> On 11/21/2017 01:12 PM, Christian Borntraeger wrote: >>>>> >>>>> >>>>> On 11/21/2017 08:30 PM, Jens Axboe wrote: >>>>>> On 11/21/2017 12:15 PM, Christian Borntraeger wrote: >>>>>>> >>>>>>> >>>>>>> On 11/21/2017 07:39 PM, Jens Axboe wrote: >>>>>>>> On 11/21/2017 11:27 AM, Jens Axboe wrote: >>>>>>>>> On 11/21/2017 11:12 AM, Christian Borntraeger wrote: >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> On 11/21/2017 07:09 PM, Jens Axboe wrote: >>>>>>>>>>> On 11/21/2017 10:27 AM, Jens Axboe wrote: >>>>>>>>>>>> On 11/21/2017 03:14 AM, Christian Borntraeger wrote: >>>>>>>>>>>>> Bisect points to >>>>>>>>>>>>> >>>>>>>>>>>>> 1b5a7455d345b223d3a4658a9e5fce985b7998c1 is the first bad commit >>>>>>>>>>>>> commit 1b5a7455d345b223d3a4658a9e5fce985b7998c1 >>>>>>>>>>>>> Author: Christoph Hellwig <hch@xxxxxx> >>>>>>>>>>>>> Date: Mon Jun 26 12:20:57 2017 +0200 >>>>>>>>>>>>> >>>>>>>>>>>>> blk-mq: Create hctx for each present CPU >>>>>>>>>>>>> >>>>>>>>>>>>> commit 4b855ad37194f7bdbb200ce7a1c7051fecb56a08 upstream. >>>>>>>>>>>>> >>>>>>>>>>>>> Currently we only create hctx for online CPUs, which can lead to a lot >>>>>>>>>>>>> of churn due to frequent soft offline / online operations. Instead >>>>>>>>>>>>> allocate one for each present CPU to avoid this and dramatically simplify >>>>>>>>>>>>> the code. >>>>>>>>>>>>> >>>>>>>>>>>>> Signed-off-by: Christoph Hellwig <hch@xxxxxx> >>>>>>>>>>>>> Reviewed-by: Jens Axboe <axboe@xxxxxxxxx> >>>>>>>>>>>>> Cc: Keith Busch <keith.busch@xxxxxxxxx> >>>>>>>>>>>>> Cc: linux-block@xxxxxxxxxxxxxxx >>>>>>>>>>>>> Cc: linux-nvme@xxxxxxxxxxxxxxxxxxx >>>>>>>>>>>>> Link: http://lkml.kernel.org/r/20170626102058.10200-3-hch@xxxxxx >>>>>>>>>>>>> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >>>>>>>>>>>>> Cc: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> >>>>>>>>>>>>> Cc: Mike Galbraith <efault@xxxxxx> >>>>>>>>>>>>> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> >>>>>>>>>>>> >>>>>>>>>>>> I wonder if we're simply not getting the masks updated correctly. I'll >>>>>>>>>>>> take a look. >>>>>>>>>>> >>>>>>>>>>> Can't make it trigger here. We do init for each present CPU, which means >>>>>>>>>>> that if I offline a few CPUs here and register a queue, those still show >>>>>>>>>>> up as present (just offline) and get mapped accordingly. >>>>>>>>>>> >>>>>>>>>>> From the looks of it, your setup is different. If the CPU doesn't show >>>>>>>>>>> up as present and it gets hotplugged, then I can see how this condition >>>>>>>>>>> would trigger. What environment are you running this in? We might have >>>>>>>>>>> to re-introduce the cpu hotplug notifier, right now we just monitor >>>>>>>>>>> for a dead cpu and handle that. >>>>>>>>>> >>>>>>>>>> I am not doing a hot unplug and the replug, I use KVM and add a previously >>>>>>>>>> not available CPU. >>>>>>>>>> >>>>>>>>>> in libvirt/virsh speak: >>>>>>>>>> <vcpu placement='static' current='1'>4</vcpu> >>>>>>>>> >>>>>>>>> So that's why we run into problems. It's not present when we load the device, >>>>>>>>> but becomes present and online afterwards. >>>>>>>>> >>>>>>>>> Christoph, we used to handle this just fine, your patch broke it. >>>>>>>>> >>>>>>>>> I'll see if I can come up with an appropriate fix. >>>>>>>> >>>>>>>> Can you try the below? >>>>>>> >>>>>>> >>>>>>> It does prevent the crash but it seems that the new CPU is not "used " after the hotplug for mq: >>>>>>> >>>>>>> >>>>>>> output with 2 cpus: >>>>>>> /sys/kernel/debug/block/vda >>>>>>> /sys/kernel/debug/block/vda/hctx0 >>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0 >>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/completed >>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/merged >>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/dispatched >>>>>>> /sys/kernel/debug/block/vda/hctx0/cpu0/rq_list >>>>>>> /sys/kernel/debug/block/vda/hctx0/active >>>>>>> /sys/kernel/debug/block/vda/hctx0/run >>>>>>> /sys/kernel/debug/block/vda/hctx0/queued >>>>>>> /sys/kernel/debug/block/vda/hctx0/dispatched >>>>>>> /sys/kernel/debug/block/vda/hctx0/io_poll >>>>>>> /sys/kernel/debug/block/vda/hctx0/sched_tags_bitmap >>>>>>> /sys/kernel/debug/block/vda/hctx0/sched_tags >>>>>>> /sys/kernel/debug/block/vda/hctx0/tags_bitmap >>>>>>> /sys/kernel/debug/block/vda/hctx0/tags >>>>>>> /sys/kernel/debug/block/vda/hctx0/ctx_map >>>>>>> /sys/kernel/debug/block/vda/hctx0/busy >>>>>>> /sys/kernel/debug/block/vda/hctx0/dispatch >>>>>>> /sys/kernel/debug/block/vda/hctx0/flags >>>>>>> /sys/kernel/debug/block/vda/hctx0/state >>>>>>> /sys/kernel/debug/block/vda/sched >>>>>>> /sys/kernel/debug/block/vda/sched/dispatch >>>>>>> /sys/kernel/debug/block/vda/sched/starved >>>>>>> /sys/kernel/debug/block/vda/sched/batching >>>>>>> /sys/kernel/debug/block/vda/sched/write_next_rq >>>>>>> /sys/kernel/debug/block/vda/sched/write_fifo_list >>>>>>> /sys/kernel/debug/block/vda/sched/read_next_rq >>>>>>> /sys/kernel/debug/block/vda/sched/read_fifo_list >>>>>>> /sys/kernel/debug/block/vda/write_hints >>>>>>> /sys/kernel/debug/block/vda/state >>>>>>> /sys/kernel/debug/block/vda/requeue_list >>>>>>> /sys/kernel/debug/block/vda/poll_stat >>>>>> >>>>>> Try this, basically just a revert. >>>>> >>>>> Yes, seems to work. >>>>> >>>>> Tested-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> >>>> >>>> Great, thanks for testing. >>>> >>>>> Do you know why the original commit made it into 4.12 stable? After all >>>>> it has no Fixes tag and no cc stable- >>>> >>>> I was wondering the same thing when you said it was in 4.12.stable and >>>> not in 4.12 release. That patch should absolutely not have gone into >>>> stable, it's not marked as such and it's not fixing a problem that is >>>> stable worthy. In fact, it's causing a regression... >>>> >>>> Greg? Upstream commit is mentioned higher up, start of the email. >>>> >>> >>> >>> Forgot to cc Greg? >> >> I did, thanks for doing that. Now I wonder how to mark this patch, >> as we should revert it from kernels that have the bad commit. 4.12 >> is fine, 4.12.later-stable is not. >> > > I think we should tag it with: > > Fixes: 4b855ad37194 ("blk-mq: Create hctx for each present CPU") > > which should bring it into 4.13 stable and 4.14 stable. 4.12 stable seems EOL anyway. Yeah, I think so too. But thinking more about this, I'm pretty sure this adds a bad lock dependency with hotplug. Need to verify so we ensure we don't introduce a potential deadlock here... -- Jens Axboe
