Re: [PATCH V7 2/3] scsi: ufs: Fix a race condition between ufshcd_abort and eh_work

From: Can Guo
Date: Wed Dec 02 2020 - 23:02:34 EST

On 2020-12-03 10:21, Stanley Chu wrote:
On Wed, 2020-12-02 at 04:04 -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@xxxxxxxxxxxxxx>
Signed-off-by: Can Guo <cang@xxxxxxxxxxxxxx>
---
drivers/scsi/ufs/ufshcd.c | 60 +++++++++++++++++++++++++++++++++++++----------
drivers/scsi/ufs/ufshcd.h | 2 ++
2 files changed, 49 insertions(+), 13 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index f0bb3fc..26c1fa0 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");

@@ -4929,9 +4943,11 @@ static void __ufshcd_transfer_req_compl(struct ufs_hba *hba,
struct scsi_cmnd *cmd;
int result;
int index;
+ bool update_scaling = false;

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) {
@@ -4944,15 +4960,17 @@ static void __ufshcd_transfer_req_compl(struct ufs_hba *hba,
/* Do not touch lrbp after scsi done */
cmd->scsi_done(cmd);
__ufshcd_release(hba);
+ update_scaling = true;
} else if (lrbp->command_type == UTP_CMD_TYPE_DEV_MANAGE ||
lrbp->command_type == UTP_CMD_TYPE_UFS_STORAGE) {
if (hba->dev_cmd.complete) {
ufshcd_add_command_trace(hba, index,
"dev_complete");
complete(hba->dev_cmd.complete);
+ update_scaling = true;
}
}
- if (ufshcd_is_clkscaling_supported(hba))
+ if (ufshcd_is_clkscaling_supported(hba) && update_scaling)
hba->clk_scaling.active_reqs--;
}

@@ -6374,8 +6392,12 @@ 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 +6469,7 @@ 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 +6719,6 @@ 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 +6739,7 @@ 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 +6758,27 @@ 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));
+ __set_bit(tag, &hba->outstanding_reqs);
+ lrbp->in_use = true;
+ hba->force_reset = true;
+ ufshcd_schedule_eh_work(hba);

ufshcd_schedule_eh_work() will set hba->ufshcd_state as
UFSHCD_STATE_EH_SCHEDULED_FATAL. While in this state,
ufshcd_queuecommand() will set_host_byte(DID_BAD_TARGET) which is
similar as what you would like to do in this patch.

Is this enough for avoiding reusing tag issue? Just wonder if
lrpb->in_use flag is really required to be added.

Hi Stanley,

Thanks for the discussion.

To be accurate, it is to prevent lrb from being re-used, not the
tag. Block layer and/or scsi layer can re-use the tag right after
we abort the cmd, but the lrb is empty since we cleared it from
abort path and we need to make sure the lrb stays empty before the
full reset and restore happens. So, in queuecommand path, we have
below checks to prevernt the lrb being re-used. This is before
hba->ufshcd_state checks.

+ 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;
+ }

In above checks, below exception is for the case that a SSU cmd
sent from PM ops is trying to re-use the lrb. In this case, we
should simply let it fail so that PM ops errors out to unblock
error handling (since error handling is serialized with PM ops).

+ if (hba->pm_op_in_progress)
+ set_host_byte(cmd, DID_BAD_TARGET);

Thanks,

Can Guo.


+ }
+ 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;
};

/**