Messages in this thread | | | Subject | Re: [PATCH v12 1/2] scsi: ufs: Enable power management for wlun | From | "Asutosh Das (asd)" <> | Date | Wed, 24 Mar 2021 19:14:53 -0700 |
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On 3/23/2021 12:19 PM, Adrian Hunter wrote: > On 23/03/21 5:13 pm, Asutosh Das (asd) wrote: >> On 3/22/2021 11:12 PM, Adrian Hunter wrote: >>> On 22/03/21 9:53 pm, Asutosh Das (asd) wrote: >>>> On 3/19/2021 10:47 AM, Adrian Hunter wrote: >>>>> On 19/03/21 2:35 am, Asutosh Das wrote: >>>>>> During runtime-suspend of ufs host, the scsi devices are >>>>>> already suspended and so are the queues associated with them. >>>>>> But the ufs host sends SSU to wlun during its runtime-suspend. >>>>>> During the process blk_queue_enter checks if the queue is not in >>>>>> suspended state. If so, it waits for the queue to resume, and never >>>>>> comes out of it. >>>>>> The commit >>>>>> (d55d15a33: scsi: block: Do not accept any requests while suspended) >>>>>> adds the check if the queue is in suspended state in blk_queue_enter(). >>>>>> >>>>>> Call trace: >>>>>> __switch_to+0x174/0x2c4 >>>>>> __schedule+0x478/0x764 >>>>>> schedule+0x9c/0xe0 >>>>>> blk_queue_enter+0x158/0x228 >>>>>> blk_mq_alloc_request+0x40/0xa4 >>>>>> blk_get_request+0x2c/0x70 >>>>>> __scsi_execute+0x60/0x1c4 >>>>>> ufshcd_set_dev_pwr_mode+0x124/0x1e4 >>>>>> ufshcd_suspend+0x208/0x83c >>>>>> ufshcd_runtime_suspend+0x40/0x154 >>>>>> ufshcd_pltfrm_runtime_suspend+0x14/0x20 >>>>>> pm_generic_runtime_suspend+0x28/0x3c >>>>>> __rpm_callback+0x80/0x2a4 >>>>>> rpm_suspend+0x308/0x614 >>>>>> rpm_idle+0x158/0x228 >>>>>> pm_runtime_work+0x84/0xac >>>>>> process_one_work+0x1f0/0x470 >>>>>> worker_thread+0x26c/0x4c8 >>>>>> kthread+0x13c/0x320 >>>>>> ret_from_fork+0x10/0x18 >>>>>> >>>>>> Fix this by registering ufs device wlun as a scsi driver and >>>>>> registering it for block runtime-pm. Also make this as a >>>>>> supplier for all other luns. That way, this device wlun >>>>>> suspends after all the consumers and resumes after >>>>>> hba resumes. >>>>>> >>>>>> Co-developed-by: Can Guo <cang@codeaurora.org> >>>>>> Signed-off-by: Can Guo <cang@codeaurora.org> >>>>>> Signed-off-by: Asutosh Das <asutoshd@codeaurora.org> >>>>> >>>>> I have some more comments that may help straighten things out. >>>>> >>>>> Also please look at ufs_debugfs_get_user_access() and >>>>> ufs_debugfs_put_user_access() that now need to scsi_autopm_get/put_device >>>>> sdev_ufs_device. >>>>> >>>>> It would also be good if you could re-base on linux-next. >>>>> >>>> >>>> Hi Adrian >>>> Thanks for the comments. >>>> >>>> I agree moving the code to wlun probe and other changes. >>>> But it looks to me that it may not fully solve the issue. >>>> >>>> Please let me explain my understanding on this: >>>> >>>> (Please refer to the logs in v10) >>>> scsi_autopm_*() are invoked on a sdev. >>>> pm_runtime_get_suppliers()/rpm_put_suppliers() are on the supplier device. >>>> >>>> For the device wlun: >>>> slave_configure(): >>>> - doesn't set the rpm_autosuspend >>>> - pm_runtime_getnoresume() >>>> scsi_sysfs_add_sdev(): >>>> - pm_runtime_forbid() >>>> - scsi_autopm_get_device() >>>> - device_add() >>>> - ufshcd_wl_probe() >>>> - scsi_autopm_put_device() >>>> >>>> For all other scsi devices: >>>> slave_alloc(): >>>> - ufshcd_setup_links() >>>> Say all link_add: pm_runtime_put(&hba->sdev_ufs_device->sdev_gendev); >>> >>> With DL_FLAG_RPM_ACTIVE, links will 'get' not 'put' >>> >> I'm referring to the pm_runtime_put(sdev_ufs_device) after all the links are setup, that you suggested to add. > > Ok > >>>> slave_configure(): >>>> - set rpm_autosuspend >>>> scsi_sysfs_add_sdev(): >>>> - scsi_autopm_get_device() >>>> - device_add() -> schedules an async probe() >>>> - scsi_autopm_put_device() - (1) >>>> >>>> Now the rpm_put_suppliers() can be invoked *after* pm_runtime_get_suppliers() of the async probe(), since both are running in different contexts. >>> >>> Only if the sd device suspends. >>> >> Correct. What'd stop the sd device from suspending? >> We should be stopping the sd device from suspending here - imho. >
Hi Adrian, Thanks for the comments.
> You mean for performance reasons. That is something we can > look at, but let's get it working first. > Not for performance reasons. I meant to say that this issue can be fixed if we stop the sd devices from suspending until the sd_probe() is completed. >> >>>> In that case, the usage_count of supplier would be decremented until rpm_active of this link becomes 1. >>> >>> Right, because the sd device suspended. >>> >>>> Now the pm_runtime_get_suppliers() expects the link_active to be more than 1. >>> >>> Not sure what you mean here. pm_runtime_*put*_suppliers() won't do anything if the link count is 1. >> I'm referring to the logs that I pasted before: >> [ 6.941267][ T7] scsi 0:0:0:4: rpm_put_suppliers: [BEF] Supp (0:0:0:49488) usage_count: 4 rpm_active: 3 >> >> ------ T196 Context comes in while T7 is running ---------- >> [ 6.941466][ T196] scsi 0:0:0:4: pm_runtime_get_suppliers: (0:0:0:49488): supp: usage_count: 5 rpm_active: 4 >> -------------------------------------------------------------- >> >> [ 7.788397][ T7] scsi 0:0:0:4: rpm_put_suppliers: [AFT] Supp (0:0:0:49488) usage_count: 2 rpm_active: 1 >> >> I meant to say that, if the rpm_put_suppliers() is invoked after the pm_runtime_get_suppliers() as is seen above then the link_active may become 1 even *after* pm_runtime_get_suppliers() is invoked. >> >> I'm referring to the pm_runtime_get_suppliers() invoked from: >> driver_probe_device() - say for, sd 0:0:0:x >> |- pm_runtime_get_suppliers() - for sd 0:0:0:49488 > > I am hoping that was the problem that Rafael's revert dealt with. > I think the issue is in the sequence of events. If rpm_put_suppliers() runs after pm_runtime_get_suppliers() this issue can occur.
>>> >>>> Now then, there comes a time, that when sd_probe() schedules a suspend, the supplier usage_count becomes 0 and the link_active becomes 1. >>>> And the supplier suspends before the consumer. >>> >>> sd probe first resumes the sd device which will resume the supplier. >>> >> Correct, but it'd again schedule a suspend (since autosuspend is enabled now) at the end of the sd_probe(). >> Thereafter, pm_runtime_put_suppliers()(sd 0:0:0:49488) is invoked from driver_probe_device() which had actually invoked sd_probe(). >> That'd make the link_active to 1 even when sd 0:0:0:x is active. > > If sd 0:0:0:x is active then rpm_get_suppliers() still has +1 rpm_active. pm_runtime_get_suppliers() also has +1 rpm_active. > i.e. rpm_active is 3. If rpm_put_suppliers() is called, it means sd 0:0:0:x has really runtime suspended (not just waiting for autosuspend. Otherwise when the probe ends pm_runtime_put_suppliers() will drop rpm_active from 3 to 2. In the good case it'd drop from 3 to 2. But in the bad case, I see that it drops to 1. That's when the supplier suspends before the consumer. That would happen when rpm_put_suppliers() runs after the pm_runtime_get_suppliers() is completed and decrements the usage_count of supplier until link_active is 1. At that point yes, sd 0:0:0:x has really runtime-suspended. sd_probe() would resume it and schedule a suspend at the end of probe.
IIUC, below is the sequence of events that can lead to this issue: 1. sd 0:0:0:x schedules an async probe 2. sd 0:0:0:x invokes scsi_autopm_put_device() 3. async probe completes pm_runtime_get_suppliers() increments the rpm_active. 4. suspend of sd 0:0:0:x is invoked and rpm_put_suppliers() is invoked which decrements the link_active (this was incremented in 3 above) 5. sd_probe() is invoked which resumes it and schedules a suspend 6. pm_runtime_put_suppliers() is invoked which decreases the link_active to 1 and supplier suspends before the consumer.
So my solution was to stop sd 0:0:0:x from runtime suspending until the sd_probe() is done.
> > But it is a bit theoretical. Let's try it and see. > >> >>>> >>>> So I was wondering, what'd make sure that the pm_runtime_get_suppliers() from driver_probe_device() is invoked after scsi_autopm_put_device() (1) finishes the rpm_put_suppliers(). >>>> >>>> Am not sure if I'm missing something in this. >>>> Do you think, the current changes alone can fix the above issue? >>> >>> Yes, but let's see. >>> >> Essentially, we should stop the sd device from runtime suspending until it's probe is done. Then allow the same. Does it make sense? >> Please let me know what you think. > > I really think it would be good to try the changes that have been identified and see how it behaves. > > Then go from there. > Sure, I've pushed the changes v13 today. I will test it after the changes are finalized.
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