Re: [PATCH V5 2/3] scsi: ufs: Fix a race condition between ufshcd_abort and eh_work

Can Guo
2020-12-02T09:11:07Z

On 2020-12-02 16:48, Stanley Chu wrote:
> Hi Can,
>
> On Wed, 2020-12-02 at 00:24 -0800, Can Guo wrote:
>> In current task abort routine, if task abort happens to the device
>> W-LU,
>> the code directly jumps to ufshcd_eh_host_reset_handler() to perform a
>> full reset and restore then returns FAIL or SUCCESS. Commands sent to
>> the
>> device W-LU are most likely the SSU cmds sent during UFS PM
>> operations. If
>> such SSU cmd enters task abort routine, when
>> ufshcd_eh_host_reset_handler()
>> flushes eh_work, it will get stuck there since err_handler is
>> serialized
>> with PM operations.
>>
>> In order to unblock above call path, we merely clean up the lrb taken
>> by
>> this cmd, queue the eh_work and return SUCCESS. Once the cmd is
>> aborted,
>> the PM operation which sends out the cmd just errors out, then
>> err_handler
>> shall be able to proceed with the full reset and restore.
>>
>> In this scenario, the cmd is aborted even before it is actually
>> cleared by
>> HW, set the lrb->in_use flag to prevent subsequent cmds, including
>> SCSI
>> cmds and dev cmds, from taking the lrb released from abort. The flag
>> shall
>> evetually be cleared in __ufshcd_transfer_req_compl() invoked by the
>> full
>> reset and restore from err_handler.
>>
>> Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
>> Signed-off-by: Can Guo <cang@codeaurora.org>
>> ---
>> drivers/scsi/ufs/ufshcd.c | 55
>> ++++++++++++++++++++++++++++++++++++-----------
>> drivers/scsi/ufs/ufshcd.h | 2 ++
>> 2 files changed, 45 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index f0bb3fc..fa90e15 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -2539,6 +2539,14 @@ static int ufshcd_queuecommand(struct Scsi_Host
>> *host, struct scsi_cmnd *cmd)
>> (hba->clk_gating.state != CLKS_ON));
>>
>> lrbp = &hba->lrb[tag];
>> + if (unlikely(lrbp->in_use)) {
>> + if (hba->pm_op_in_progress)
>> + set_host_byte(cmd, DID_BAD_TARGET);
>> + else
>> + err = SCSI_MLQUEUE_HOST_BUSY;
>> + ufshcd_release(hba);
>> + goto out;
>> + }
>>
>> WARN_ON(lrbp->cmd);
>> lrbp->cmd = cmd;
>> @@ -2781,6 +2789,11 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba
>> *hba,
>>
>> init_completion(&wait);
>> lrbp = &hba->lrb[tag];
>> + if (unlikely(lrbp->in_use)) {
>> + err = -EBUSY;
>> + goto out;
>> + }
>> +
>> WARN_ON(lrbp->cmd);
>> err = ufshcd_compose_dev_cmd(hba, lrbp, cmd_type, tag);
>> if (unlikely(err))
>> @@ -2797,6 +2810,7 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba
>> *hba,
>>
>> err = ufshcd_wait_for_dev_cmd(hba, lrbp, timeout);
>>
>> +out:
>> ufshcd_add_query_upiu_trace(hba, tag,
>> err ? "query_complete_err" : "query_complete");
>>
>> @@ -4932,6 +4946,7 @@ static void __ufshcd_transfer_req_compl(struct
>> ufs_hba *hba,
>>
>> for_each_set_bit(index, &completed_reqs, hba->nutrs) {
>> lrbp = &hba->lrb[index];
>> + lrbp->in_use = false;
>> lrbp->compl_time_stamp = ktime_get();
>> cmd = lrbp->cmd;
>> if (cmd) {
>> @@ -6374,8 +6389,12 @@ static int ufshcd_issue_devman_upiu_cmd(struct
>> ufs_hba *hba,
>>
>> init_completion(&wait);
>> lrbp = &hba->lrb[tag];
>> - WARN_ON(lrbp->cmd);
>> + if (unlikely(lrbp->in_use)) {
>> + err = -EBUSY;
>> + goto out;
>> + }
>>
>> + WARN_ON(lrbp->cmd);
>> lrbp->cmd = NULL;
>> lrbp->sense_bufflen = 0;
>> lrbp->sense_buffer = NULL;
>> @@ -6447,6 +6466,7 @@ static int ufshcd_issue_devman_upiu_cmd(struct
>> ufs_hba *hba,
>> }
>> }
>>
>> +out:
>> blk_put_request(req);
>> out_unlock:
>> up_read(&hba->clk_scaling_lock);
>> @@ -6696,16 +6716,6 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
>> BUG();
>> }
>>
>> - /*
>> - * Task abort to the device W-LUN is illegal. When this command
>> - * will fail, due to spec violation, scsi err handling next step
>> - * will be to send LU reset which, again, is a spec violation.
>> - * To avoid these unnecessary/illegal step we skip to the last error
>> - * handling stage: reset and restore.
>> - */
>> - if (lrbp->lun == UFS_UPIU_UFS_DEVICE_WLUN)
>> - return ufshcd_eh_host_reset_handler(cmd);
>> -
>> ufshcd_hold(hba, false);
>> reg = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
>> /* If command is already aborted/completed, return SUCCESS */
>> @@ -6726,7 +6736,7 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
>> * to reduce repeated printouts. For other aborted requests only
>> print
>> * basic details.
>> */
>> - scsi_print_command(hba->lrb[tag].cmd);
>> + scsi_print_command(cmd);
>> if (!hba->req_abort_count) {
>> ufshcd_update_reg_hist(&hba->ufs_stats.task_abort, 0);
>> ufshcd_print_host_regs(hba);
>> @@ -6745,6 +6755,27 @@ static int ufshcd_abort(struct scsi_cmnd *cmd)
>> goto cleanup;
>> }
>>
>> + /*
>> + * Task abort to the device W-LUN is illegal. When this command
>> + * will fail, due to spec violation, scsi err handling next step
>> + * will be to send LU reset which, again, is a spec violation.
>> + * To avoid these unnecessary/illegal steps, first we clean up
>> + * the lrb taken by this cmd and mark the lrb as in_use, then
>> + * queue the eh_work and bail.
>> + */
>> + if (lrbp->lun == UFS_UPIU_UFS_DEVICE_WLUN) {
>> + spin_lock_irqsave(host->host_lock, flags);
>> + if (lrbp->cmd) {
>> + __ufshcd_transfer_req_compl(hba, (1UL << tag));
>
> The timed out "tag" is cleared once here.
>
>> + __set_bit(tag, &hba->outstanding_reqs);
>> + lrbp->in_use = true;
>> + hba->force_reset = true;
>> + ufshcd_schedule_eh_work(hba);
>
> The same "tag" would be cleared again in error handler with
> __ufshcd_transfer_req_compl().
>
> In __ufshcd_transfer_req_compl, hba->clk_scaling.active_reqs will be
> decreased if clk-scaling is supported as below,
>
> if (ufshcd_is_clkscaling_supported(hba))
> hba->clk_scaling.active_reqs--;
>
> Will be the hba->clk_scaling.active_reqs value become abnormal by this
> flow?
>

Yes, it may undershoot. Actually the logic in
__ufshcd_transfer_req_compl()
should be updated - clk_scaling.active_reqs should be updated only when
there are cmds (scsi or query) to complete. Here is not the only place
which
can cause a undershoot. We can prevent the undershoot with below check.

if (ufshcd_is_clkscaling_supported(hba) &&
hba->clk_scaling.active_reqs > 0)
hba->clk_scaling.active_reqs--;

Thanks,

Can Guo.

> Thanks,
> Stanley Chu
>
>> + }
>> + spin_unlock_irqrestore(host->host_lock, flags);
>> + goto out;
>> + }
>> +
>> /* Skip task abort in case previous aborts failed and report failure
>> */
>> if (lrbp->req_abort_skip)
>> err = -EIO;
>> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
>> index 1e680bf..66e5338 100644
>> --- a/drivers/scsi/ufs/ufshcd.h
>> +++ b/drivers/scsi/ufs/ufshcd.h
>> @@ -163,6 +163,7 @@ struct ufs_pm_lvl_states {
>> * @crypto_key_slot: the key slot to use for inline crypto (-1 if
>> none)
>> * @data_unit_num: the data unit number for the first block for
>> inline crypto
>> * @req_abort_skip: skip request abort task flag
>> + * @in_use: indicates that this lrb is still in use
>> */
>> struct ufshcd_lrb {
>> struct utp_transfer_req_desc *utr_descriptor_ptr;
>> @@ -192,6 +193,7 @@ struct ufshcd_lrb {
>> #endif
>>
>> bool req_abort_skip;
>> + bool in_use;
>> };
>>
>> /**