[PATCH v2] scsi: ufs: core: Quiesce SCSI devices instead of host tagset during error handling

[Stanley Jhu <stanleyjhu@google.com>]

Commit 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()")
switched UFS internal commands to allocate requests on
hba->host->pseudo_sdev->request_queue, which shares the host tagset with
regular LUNs.

During error recovery, ufshcd_err_handling_prepare() calls
blk_mq_quiesce_tagset(&hba->host->tag_set), marking all queues in the
tagset as quiesced, including pseudo_sdev->request_queue. When
ufshcd_verify_dev_init() subsequently issues internal commands (e.g. NOP
OUT UPIU) via blk_execute_rq(), blk_mq_run_hw_queue() skips running the
quiesced queue, resulting in an unrecoverable circular wait deadlock.

Resolve this by quiescing only the logical units attached to the host via
shost_for_each_device() during error handling. Because
shost_for_each_device() skips pseudo SCSI devices (via
scsi_device_is_pseudo_dev() in __scsi_iterate_devices()), pseudo_sdev
stays unquiesced and internal commands can be dispatched and completed.

Keeping the logical units quiesced preserves behaviour that predates the
current call. Until commit 2a36646012fc ("scsi: ufs: core: Simplify
ufshcd_err_handling_prepare()"), the prepare path called
ufshcd_scsi_block_requests() to hold off new commands in addition to
blk_mq_wait_quiesce_done() to wait for the ongoing ones; folding both
into blk_mq_quiesce_tagset() kept that behaviour. Waiting without
quiescing would drop the first half, so the queues stay quiesced here.

Clock scaling and command pause (ufshcd_pause_command_processing) paths
continue to use blk_mq_quiesce_tagset() as they require freezing all
queues including internal commands.

Fixes: 08b12cda6c44 ("scsi: ufs: core: Switch to scsi_get_internal_cmd()")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/6f78c4bd-a70b-402d-abfd-599091b67674@acm.org/
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Stanley Jhu <stanleyjhu@google.com>
---
v2:
- Commit message only; no functional change.
- Fix the Link: tag, which cited a Message-ID that is not in the archive.
- Explain why the logical units stay quiesced, referring to the behaviour
  that predates 2a36646012fc, instead of the vague claim about retry storms.

 drivers/ufs/core/ufshcd.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index a25b6a0cb5c6..1ca731675ad1 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -6781,6 +6781,23 @@ static void ufshcd_clk_scaling_suspend(struct ufs_hba *hba, bool suspend)
 	}
 }
 
+static void ufshcd_quiesce_all_sdevs(struct ufs_hba *hba)
+{
+	struct scsi_device *sdev;
+
+	shost_for_each_device(sdev, hba->host)
+		blk_mq_quiesce_queue_nowait(sdev->request_queue);
+	blk_mq_wait_quiesce_done(&hba->host->tag_set);
+}
+
+static void ufshcd_unquiesce_all_sdevs(struct ufs_hba *hba)
+{
+	struct scsi_device *sdev;
+
+	shost_for_each_device(sdev, hba->host)
+		blk_mq_unquiesce_queue(sdev->request_queue);
+}
+
 static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
 {
 	/*
@@ -6816,13 +6833,13 @@ static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
 		ufshcd_clk_scaling_allow(hba, false);
 	}
 	/* Wait for ongoing ufshcd_queuecommand() calls to finish. */
-	blk_mq_quiesce_tagset(&hba->host->tag_set);
+	ufshcd_quiesce_all_sdevs(hba);
 	cancel_work_sync(&hba->eeh_work);
 }
 
 static void ufshcd_err_handling_unprepare(struct ufs_hba *hba)
 {
-	blk_mq_unquiesce_tagset(&hba->host->tag_set);
+	ufshcd_unquiesce_all_sdevs(hba);
 	ufshcd_release(hba);
 	if (ufshcd_is_clkscaling_supported(hba))
 		ufshcd_clk_scaling_suspend(hba, false);
-- 
2.55.0.1007.g17ff1f9808-goog