Messages in this thread Patch in this message | | | Date | Tue, 03 Nov 2020 18:01:01 +0800 | From | Can Guo <> | Subject | Re: [PATCH v1 1/2] scsi: ufs: Fix unbalanced scsi_block_reqs_cnt caused by ufshcd_hold() |
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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,
Can Guo.
>> ufshcd_ungate_work() in a paired way, increase it only if queue_work() >> returns true. >> >> Signed-off-by: Can Guo <cang@codeaurora.org> >> Reviewed-by: Hongwu Su <hongwus@codeaurora.org> >> --- >> 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
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