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Subject[PATCH 1/1] scsi: ufs: add reference counting for scsi block requests
Date
From: Subhash Jadavani <subhashj@codeaurora.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@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
---
drivers/scsi/ufs/ufshcd.c | 44 +++++++++++++++++++++++++++++++++++++-------
drivers/scsi/ufs/ufshcd.h | 5 +++++
2 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 8af2af3..a9ebc8d 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -264,6 +264,36 @@ static inline void ufshcd_disable_irq(struct ufs_hba *hba)
}
}

+void ufshcd_scsi_unblock_requests(struct ufs_hba *hba)
+{
+ unsigned long flags;
+ bool unblock = false;
+
+ spin_lock_irqsave(hba->host->host_lock, flags);
+ hba->scsi_block_reqs_cnt--;
+ unblock = !hba->scsi_block_reqs_cnt;
+ spin_unlock_irqrestore(hba->host->host_lock, flags);
+ if (unblock)
+ scsi_unblock_requests(hba->host);
+}
+EXPORT_SYMBOL(ufshcd_scsi_unblock_requests);
+
+static inline void __ufshcd_scsi_block_requests(struct ufs_hba *hba)
+{
+ if (!hba->scsi_block_reqs_cnt++)
+ scsi_block_requests(hba->host);
+}
+
+void ufshcd_scsi_block_requests(struct ufs_hba *hba)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(hba->host->host_lock, flags);
+ __ufshcd_scsi_block_requests(hba);
+ spin_unlock_irqrestore(hba->host->host_lock, flags);
+}
+EXPORT_SYMBOL(ufshcd_scsi_block_requests);
+
/* replace non-printable or non-ASCII characters with spaces */
static inline void ufshcd_remove_non_printable(char *val)
{
@@ -1079,12 +1109,12 @@ 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;
@@ -1093,7 +1123,7 @@ 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);
}

/**
@@ -1413,7 +1443,7 @@ 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);
}

/**
@@ -1469,7 +1499,7 @@ 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);
@@ -5178,7 +5208,7 @@ 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);
}
@@ -5280,7 +5310,7 @@ 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;

diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 1332e54..84f4175 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;
@@ -679,6 +680,7 @@ struct ufs_hba {

struct rw_semaphore clk_scaling_lock;
struct ufs_desc_size desc_size;
+ int scsi_block_reqs_cnt;
};

/* Returns true if clocks can be gated. Otherwise false */
@@ -851,6 +853,9 @@ int ufshcd_map_desc_id_to_length(struct ufs_hba *hba, enum desc_idn desc_id,

u32 ufshcd_get_local_unipro_ver(struct ufs_hba *hba);

+void ufshcd_scsi_block_requests(struct ufs_hba *hba);
+void ufshcd_scsi_unblock_requests(struct ufs_hba *hba);
+
/* Wrapper functions for safely calling variant operations */
static inline const char *ufshcd_get_var_name(struct ufs_hba *hba)
{
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
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