[PATCH v3] scsi: ufs: core: Keep internal commands dispatchable 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.

Keep quiescing the tagset and unquiesce the pseudo SCSI device on top of
that, so internal commands stay dispatchable while the logical units
remain quiesced. Re-quiesce the pseudo device before unquiescing the
tagset so that quiesce_depth stays balanced.

Clock scaling and ufshcd_pause_command_processing() are unaffected: they
keep quiescing the whole tagset, internal commands included.

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/
Signed-off-by: Stanley Jhu <stanleyjhu@google.com>
---
Changes since v2:
- Keep blk_mq_quiesce_tagset() and unquiesce only the pseudo SCSI device,
  instead of iterating over SCSI devices, which skipped devices already
  being removed and left their request queues quiesced.
- Dropped Bart's Reviewed-by since the implementation changed.

 drivers/ufs/core/ufshcd.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index a25b6a0cb5c6..91270f8e45a2 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -6817,11 +6817,17 @@ static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
 	}
 	/* Wait for ongoing ufshcd_queuecommand() calls to finish. */
 	blk_mq_quiesce_tagset(&hba->host->tag_set);
+	/*
+	 * Internal commands are submitted on the pseudo SCSI device. Let them
+	 * through so that the error handler can recover the link.
+	 */
+	blk_mq_unquiesce_queue(hba->host->pseudo_sdev->request_queue);
 	cancel_work_sync(&hba->eeh_work);
 }
 
 static void ufshcd_err_handling_unprepare(struct ufs_hba *hba)
 {
+	blk_mq_quiesce_queue_nowait(hba->host->pseudo_sdev->request_queue);
 	blk_mq_unquiesce_tagset(&hba->host->tag_set);
 	ufshcd_release(hba);
 	if (ufshcd_is_clkscaling_supported(hba))
-- 
2.55.0.1007.g17ff1f9808-goog