linux-kernel - Re: [PATCH] scsi: ufs: core: quiesce request queues before check pending cmds

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Message-ID: <d3fc4d2b-81b0-4ab2-9606-5f4a5fb8b867@acm.org>
Date: Thu, 20 Jun 2024 13:57:42 -0700
From: Bart Van Assche <bvanassche@....org>
To: Ziqi Chen <quic_ziqichen@...cinc.com>, quic_cang@...cinc.com,
 mani@...nel.org, beanhuo@...ron.com, avri.altman@....com,
 junwoo80.lee@...sung.com, martin.petersen@...cle.com,
 quic_nguyenb@...cinc.com, quic_nitirawa@...cinc.com,
 quic_rampraka@...cinc.com
Cc: linux-scsi@...r.kernel.org, Alim Akhtar <alim.akhtar@...sung.com>,
 "James E.J. Bottomley" <jejb@...ux.ibm.com>,
 Peter Wang <peter.wang@...iatek.com>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Maramaina Naresh <quic_mnaresh@...cinc.com>,
 Asutosh Das <quic_asutoshd@...cinc.com>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scsi: ufs: core: quiesce request queues before check
 pending cmds

On 6/7/24 3:06 AM, Ziqi Chen wrote:
> Fix this race condition by quiescing the request queues before calling
> ufshcd_pending_cmds() so that block layer won't touch the budget map
> when ufshcd_pending_cmds() is working on it. In addition, remove the
> scsi layer blocking/unblocking to reduce redundancies and latencies.

Can you please help with testing whether the patch below would be a good
alternative to your patch (compile-tested only)?

Thanks,

Bart.

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index aa00978c6c0e..1d981283b03c 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -332,14 +332,12 @@ static void ufshcd_configure_wb(struct ufs_hba *hba)

  static void ufshcd_scsi_unblock_requests(struct ufs_hba *hba)
  {
-	if (atomic_dec_and_test(&hba->scsi_block_reqs_cnt))
-		scsi_unblock_requests(hba->host);
+	blk_mq_quiesce_tagset(&hba->host->tag_set);
  }

  static void ufshcd_scsi_block_requests(struct ufs_hba *hba)
  {
-	if (atomic_inc_return(&hba->scsi_block_reqs_cnt) == 1)
-		scsi_block_requests(hba->host);
+	blk_mq_unquiesce_tagset(&hba->host->tag_set);
  }

  static void ufshcd_add_cmd_upiu_trace(struct ufs_hba *hba, unsigned int tag,
@@ -10590,7 +10588,7 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)

  	/* Hold auto suspend until async scan completes */
  	pm_runtime_get_sync(dev);
-	atomic_set(&hba->scsi_block_reqs_cnt, 0);
+
  	/*
  	 * We are assuming that device wasn't put in sleep/power-down
  	 * state exclusively during the boot stage before kernel.
diff --git a/include/ufs/ufshcd.h b/include/ufs/ufshcd.h
index 443afb97a637..58705994fc46 100644
--- a/include/ufs/ufshcd.h
+++ b/include/ufs/ufshcd.h
@@ -889,7 +889,6 @@ enum ufshcd_mcq_opr {
   * @wb_mutex: used to serialize devfreq and sysfs write booster toggling
   * @clk_scaling_lock: used to serialize device commands and clock scaling
   * @desc_size: descriptor sizes reported by device
- * @scsi_block_reqs_cnt: reference counting for scsi block requests
   * @bsg_dev: struct device associated with the BSG queue
   * @bsg_queue: BSG queue associated with the UFS controller
   * @rpm_dev_flush_recheck_work: used to suspend from RPM (runtime power
@@ -1050,7 +1049,6 @@ struct ufs_hba {

  	struct mutex wb_mutex;
  	struct rw_semaphore clk_scaling_lock;
-	atomic_t scsi_block_reqs_cnt;

  	struct device		bsg_dev;
  	struct request_queue	*bsg_queue;