Hi Can, On Tue, 2020-11-03 at 18:01 +0800, Can Guo wrote: > On 2020-11-03 15:07, Stanley Chu wrote: > > Hi Can, > > > > On Mon, 2020-11-02 at 22:24 -0800, Can Guo wrote: > >> The scsi_block_reqs_cnt increased in ufshcd_hold() is supposed to be > >> decreased back in ufshcd_ungate_work() in a paired way. However, if > >> specific ufshcd_hold/release sequences are met, it is possible that > >> scsi_block_reqs_cnt is increased twice but only one ungate work is > >> queued. To make sure scsi_block_reqs_cnt is handled by ufshcd_hold() > >> and > > > > Just curious that how could this be possible? Would you have some > > failed > > examples? > > > > [1] One gate_work() is in the workqueue, not yet executed, now clk state > == REQ_CLKS_OFF. > [2] ufshcd_queuecommand() calls ufshcd_hold(async == ture) -> > active_req++ -> scsi_block_reqs_cnt++ -> REQ_CLKS_ON -> queue ungate > work -> active_req-- -> return -EAGAIN. > [3] Now gate_work() starts to run, but since the clk state is > REQ_CLKS_ON, gate_work() just sets clk state to CLKS_ON and bail. > [3] Someone calls ufshcd_hold(async == false) -> do something -> > ufshcd_release() -> clk state is changed to REQ_CLKS_OFF. Note that, > till now, ungate_work() is still in the work queue, not executed yet. > [4] Now, if someone calls ufshcd_hold(), we will hit the issue. > > Above sequence is a very common clk gate/ungate sequence. The issue > is because ungate_work is queued but cannot be executed in time. In my > case, I see the ungate_work is somehow delayed for about 150ms. This > change has been tested by customers on multiple platforms. And you > can tell from the code that it won't break anything. :) Thanks so much for the details. Looks good to me. Reviewed-by: Stanley Chu <stanley.chu@xxxxxxxxxxxx> > > Thanks, > > Can Guo. > > >> ufshcd_ungate_work() in a paired way, increase it only if queue_work() > >> returns true. > >> > >> Signed-off-by: Can Guo <cang@xxxxxxxxxxxxxx> > >> Reviewed-by: Hongwu Su <hongwus@xxxxxxxxxxxxxx> > >> --- > >> drivers/scsi/ufs/ufshcd.c | 6 +++--- > >> 1 file changed, 3 insertions(+), 3 deletions(-) > >> > >> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c > >> index 847f355..efa7d86 100644 > >> --- a/drivers/scsi/ufs/ufshcd.c > >> +++ b/drivers/scsi/ufs/ufshcd.c > >> @@ -1634,12 +1634,12 @@ int ufshcd_hold(struct ufs_hba *hba, bool > >> async) > >> */ > >> /* fallthrough */ > >> case CLKS_OFF: > >> - ufshcd_scsi_block_requests(hba); > >> hba->clk_gating.state = REQ_CLKS_ON; > >> trace_ufshcd_clk_gating(dev_name(hba->dev), > >> hba->clk_gating.state); > >> - queue_work(hba->clk_gating.clk_gating_workq, > >> - &hba->clk_gating.ungate_work); > >> + if (queue_work(hba->clk_gating.clk_gating_workq, > >> + &hba->clk_gating.ungate_work)) > >> + ufshcd_scsi_block_requests(hba); > >> /* > >> * fall through to check if we should wait for this > >> * work to be done or not. > > > > Thanks, > > Stanley Chu
