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Date: Wed, 16 May 2018 14:13:04 -0700
From: Subhash Jadavani <subhashj@...eaurora.org>
To: Asutosh Das <asutoshd@...eaurora.org>
Cc: cang@...eaurora.org, vivek.gautam@...eaurora.org,
rnayak@...eaurora.org, vinholikatti@...il.com,
jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com,
linux-mmc@...r.kernel.org, linux-scsi@...r.kernel.org,
linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-scsi-owner@...r.kernel.org
Subject: Re: [PATCH v2 06/10] scsi: ufs: add reference counting for scsi block
requests
On 2018-05-03 04:07, Asutosh Das wrote:
> From: Subhash Jadavani <subhashj@...eaurora.org>
>
> Currently we call the scsi_block_requests()/scsi_unblock_requests()
> whenever we want to block/unblock scsi requests but as there is no
> reference counting, nesting of these calls could leave us in undesired
> state sometime. Consider following call flow sequence:
> 1. func1() calls scsi_block_requests() but calls func2() before
> calling scsi_unblock_requests()
> 2. func2() calls scsi_block_requests()
> 3. func2() calls scsi_unblock_requests()
> 4. func1() calls scsi_unblock_requests()
>
> As there is no reference counting, we will have scsi requests unblocked
> after #3 instead of it to be unblocked only after #4. Though we may not
> have failures seen with this, we might run into some failures in
> future.
> Better solution would be to fix this by adding reference counting.
>
> Signed-off-by: Subhash Jadavani <subhashj@...eaurora.org>
> Signed-off-by: Can Guo <cang@...eaurora.org>
> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
> ---
> drivers/scsi/ufs/ufshcd.c | 28 ++++++++++++++++++++--------
> drivers/scsi/ufs/ufshcd.h | 2 ++
> 2 files changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index dfeb194..c35a076 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -264,6 +264,18 @@ static inline void ufshcd_disable_irq(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);
> +}
> +
> +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);
> +}
> +
> /* replace non-printable or non-ASCII characters with spaces */
> static inline void ufshcd_remove_non_printable(char *val)
> {
> @@ -1077,12 +1089,12 @@ static int ufshcd_clock_scaling_prepare(struct
> ufs_hba *hba)
> * make sure that there are no outstanding requests when
> * clock scaling is in progress
> */
> - scsi_block_requests(hba->host);
> + ufshcd_scsi_block_requests(hba);
> down_write(&hba->clk_scaling_lock);
> if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
> ret = -EBUSY;
> up_write(&hba->clk_scaling_lock);
> - scsi_unblock_requests(hba->host);
> + ufshcd_scsi_unblock_requests(hba);
> }
>
> return ret;
> @@ -1091,7 +1103,7 @@ static int ufshcd_clock_scaling_prepare(struct
> ufs_hba *hba)
> static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
> {
> up_write(&hba->clk_scaling_lock);
> - scsi_unblock_requests(hba->host);
> + ufshcd_scsi_unblock_requests(hba);
> }
>
> /**
> @@ -1411,7 +1423,7 @@ static void ufshcd_ungate_work(struct work_struct
> *work)
> hba->clk_gating.is_suspended = false;
> }
> unblock_reqs:
> - scsi_unblock_requests(hba->host);
> + ufshcd_scsi_unblock_requests(hba);
> }
>
> /**
> @@ -1467,7 +1479,7 @@ int ufshcd_hold(struct ufs_hba *hba, bool async)
> * work and to enable clocks.
> */
> case CLKS_OFF:
> - scsi_block_requests(hba->host);
> + ufshcd_scsi_block_requests(hba);
> hba->clk_gating.state = REQ_CLKS_ON;
> trace_ufshcd_clk_gating(dev_name(hba->dev),
> hba->clk_gating.state);
> @@ -5192,7 +5204,7 @@ static void ufshcd_err_handler(struct work_struct
> *work)
>
> out:
> spin_unlock_irqrestore(hba->host->host_lock, flags);
> - scsi_unblock_requests(hba->host);
> + ufshcd_scsi_unblock_requests(hba);
> ufshcd_release(hba);
> pm_runtime_put_sync(hba->dev);
> }
> @@ -5294,7 +5306,7 @@ static void ufshcd_check_errors(struct ufs_hba
> *hba)
> /* handle fatal errors only when link is functional */
> if (hba->ufshcd_state == UFSHCD_STATE_OPERATIONAL) {
> /* block commands from scsi mid-layer */
> - scsi_block_requests(hba->host);
> + ufshcd_scsi_block_requests(hba);
>
> hba->ufshcd_state = UFSHCD_STATE_EH_SCHEDULED;
>
> @@ -8017,7 +8029,7 @@ 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/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index 0417c42..76c31d5 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -498,6 +498,7 @@ struct ufs_stats {
> * @urgent_bkops_lvl: keeps track of urgent bkops level for device
> * @is_urgent_bkops_lvl_checked: keeps track if the urgent bkops level
> for
> * device is known or not.
> + * @scsi_block_reqs_cnt: reference counting for scsi block requests
> */
> struct ufs_hba {
> void __iomem *mmio_base;
> @@ -698,6 +699,7 @@ struct ufs_hba {
>
> struct rw_semaphore clk_scaling_lock;
> struct ufs_desc_size desc_size;
> + atomic_t scsi_block_reqs_cnt;
> };
>
> /* Returns true if clocks can be gated. Otherwise false */
Looks good to me.
--
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