Messages in this thread | | | Date | Mon, 03 Feb 2020 14:23:15 +0800 | From | Can Guo <> | Subject | Re: [PATCH v4 1/8] scsi: ufs: Flush exception event before suspend |
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On 2020-01-26 11:29, Bart Van Assche wrote: > On 2020-01-22 23:25, Can Guo wrote: >> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c >> index 1201578..c2de29f 100644 >> --- a/drivers/scsi/ufs/ufshcd.c >> +++ b/drivers/scsi/ufs/ufshcd.c >> @@ -4760,8 +4760,15 @@ static void ufshcd_slave_destroy(struct >> scsi_device *sdev) >> * UFS device needs urgent BKOPs. >> */ >> if (!hba->pm_op_in_progress && >> - ufshcd_is_exception_event(lrbp->ucd_rsp_ptr)) >> - schedule_work(&hba->eeh_work); >> + ufshcd_is_exception_event(lrbp->ucd_rsp_ptr)) { >> + /* >> + * Prevent suspend once eeh_work is scheduled >> + * to avoid deadlock between ufshcd_suspend >> + * and exception event handler. >> + */ >> + if (schedule_work(&hba->eeh_work)) >> + pm_runtime_get_noresume(hba->dev); >> + } > > Please combine the two logical tests with "&&" instead of nesting two > if-statements inside each other. > >> 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? > > Thanks, > > Bart.
Hi Bart,
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.
Thanks,
Can Guo.
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