Messages in this thread | | | Date | Tue, 04 Feb 2020 14:28:24 +0800 | From | Can Guo <> | Subject | Re: [PATCH v4 1/8] scsi: ufs: Flush exception event before suspend |
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On 2020-02-04 11:12, Bart Van Assche wrote: > On 2020-02-02 22:23, Can Guo wrote: >> On 2020-01-26 11:29, Bart Van Assche wrote: >>> On 2020-01-22 23:25, Can Guo wrote: >>>> break; >>>> case UPIU_TRANSACTION_REJECT_UPIU: >>>> /* TODO: handle Reject UPIU Response */ >>>> @@ -5215,7 +5222,14 @@ static void >>>> ufshcd_exception_event_handler(struct work_struct *work) >>>> >>>> out: >>>> scsi_unblock_requests(hba->host); >>>> - pm_runtime_put_sync(hba->dev); >>>> + /* >>>> + * pm_runtime_get_noresume is called while scheduling >>>> + * eeh_work to avoid suspend racing with exception work. >>>> + * Hence decrement usage counter using pm_runtime_put_noidle >>>> + * to allow suspend on completion of exception event handler. >>>> + */ >>>> + pm_runtime_put_noidle(hba->dev); >>>> + pm_runtime_put(hba->dev); >>>> return; >>>> } >>>> >>>> @@ -7901,6 +7915,7 @@ static int ufshcd_suspend(struct ufs_hba *hba, >>>> enum ufs_pm_op pm_op) >>>> goto enable_gating; >>>> } >>>> >>>> + flush_work(&hba->eeh_work); >>>> ret = ufshcd_link_state_transition(hba, req_link_state, 1); >>>> if (ret) >>>> goto set_dev_active; >>> >>> I think this patch introduces a new race condition, namely the >>> following: >>> - ufshcd_slave_destroy() tests pm_op_in_progress and reads the value >>> zero from that variable. >>> - ufshcd_suspend() sets hba->pm_op_in_progress to one. >>> - ufshcd_slave_destroy() calls schedule_work(). >>> >>> How about fixing this race condition by calling >>> pm_runtime_get_noresume() before checking pm_op_in_progress and by >>> reallowing resume if no work is scheduled? >> >> If you apply this patch, you will find the change is not in >> ufshcd_slave_destroy(), but in ufshcd_transfer_rsp_status(). >> So the racing you mentioned above does not exist. > > Hi Can, > > Apparently I got a function name wrong. Can the following race > condition > happen: > - ufshcd_transfer_rsp_status() tests pm_op_in_progress and reads the > value zero from that variable. > - ufshcd_suspend() sets hba->pm_op_in_progress to one. > - ufshcd_suspend() calls flush_work(&hba->eeh_work). > - ufshcd_transfer_rsp_status() calls schedule_work(&hba->eeh_work). > > Thanks, > > Bart.
Hi Bart,
The sequence you mentioned is not possible.
In normal cases, before ufshcd_transfer_rsp_status() returns, ufshcd_suspend() would not be called (unless you intentionally call ufshcd_suspend() to screw it). Because ufshcd_transfer_rsp_status() is called from __ufshcd_transfer_req_compl(), which is being used by either UFS IRQ handler or err handler. Meanwhile, in __ufshcd_transfer_req_compl(), scsi_done() is called only after ufshcd_transfer_rsp_status() returns. When we are here, it means UFS driver is still handling requests/tasks, so suspend would not kick start at this moment, either runtime suspend or system suspend.
And this is why below lines work, calling pm_runtime_get_noresume() within ufshcd_transfer_rsp_status() can prevent runtime suspend from happening after we leave ufshcd_transfer_rsp_status().
+ if (schedule_work(&hba->eeh_work)) + pm_runtime_get_noresume(hba->dev);
Thanks,
Can Guo.
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