On Tue, Jul 26, 2022 at 05:14:33PM +0800, peter.wang@xxxxxxxxxxxx wrote:
> From: Peter Wang <peter.wang@xxxxxxxxxxxx>
>
> There have a lockdep warning like below in current flow.
> kworker/u16:0: Possible unsafe locking scenario:
>
> kworker/u16:0: CPU0 CPU1
> kworker/u16:0: ---- ----
> kworker/u16:0: lock(&hba->clk_scaling_lock);
> kworker/u16:0: lock(&hba->dev_cmd.lock);
> kworker/u16:0: lock(&hba->clk_scaling_lock);
> kworker/u16:0: lock(&hba->dev_cmd.lock);
> kworker/u16:0:
>
> Before this patch clk_scaling_lock was held in reader mode during the ufshcd_wb_toggle() call.
> With this patch applied clk_scaling_lock is not held while ufshcd_wb_toggle() is called.
>
> This is safe because ufshcd_wb_toggle will held clk_scaling_lock in reader mode "again" in flow
> ufshcd_wb_toggle -> __ufshcd_wb_toggle -> ufshcd_query_flag_retry -> ufshcd_query_flag ->
> ufshcd_exec_dev_cmd -> down_read(&hba->clk_scaling_lock);
> The protect should enough and make sure clock is not change while send command.
>
> ufshcd_wb_toggle can protected by hba->clk_scaling.is_allowed to make sure
> ufshcd_devfreq_scale function not run concurrently.
>
> Fixes: 0e9d4ca43ba8 ("scsi: ufs: Protect some contexts from unexpected clock scaling")
> Signed-off-by: Peter Wang <peter.wang@xxxxxxxxxxxx>
> ---
> drivers/ufs/core/ufshcd.c | 27 ++++++++++++++++-----------
> 1 file changed, 16 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index c7b337480e3e..aa57126fdb49 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -272,6 +272,7 @@ static void ufshcd_wb_toggle_flush_during_h8(struct ufs_hba *hba, bool set);
> static inline void ufshcd_wb_toggle_flush(struct ufs_hba *hba, bool enable);
> static void ufshcd_hba_vreg_set_lpm(struct ufs_hba *hba);
> static void ufshcd_hba_vreg_set_hpm(struct ufs_hba *hba);
> +static void ufshcd_clk_scaling_allow(struct ufs_hba *hba, bool allow);
>
> static inline void ufshcd_enable_irq(struct ufs_hba *hba)
> {
> @@ -1249,12 +1250,10 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
> return ret;
> }
>
> -static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
> +static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
> {
> - if (writelock)
> - up_write(&hba->clk_scaling_lock);
> - else
> - up_read(&hba->clk_scaling_lock);
> + up_write(&hba->clk_scaling_lock);
> +
> ufshcd_scsi_unblock_requests(hba);
> ufshcd_release(hba);
> }
> @@ -1271,7 +1270,7 @@ static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool writelock)
> static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
> {
> int ret = 0;
> - bool is_writelock = true;
> + bool wb_toggle = false;
>
> ret = ufshcd_clock_scaling_prepare(hba);
> if (ret)
> @@ -1300,13 +1299,19 @@ static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
> }
> }
>
> - /* Enable Write Booster if we have scaled up else disable it */
> - downgrade_write(&hba->clk_scaling_lock);
> - is_writelock = false;
> - ufshcd_wb_toggle(hba, scale_up);
> + /* Disable clk_scaling until ufshcd_wb_toggle finish */
> + hba->clk_scaling.is_allowed = false;
> + wb_toggle = true;
>
> out_unprepare:
> - ufshcd_clock_scaling_unprepare(hba, is_writelock);
> + ufshcd_clock_scaling_unprepare(hba);
> +
> + /* Enable Write Booster if we have scaled up else disable it */
> + if (wb_toggle) {
> + ufshcd_wb_toggle(hba, scale_up);
> + ufshcd_clk_scaling_allow(hba, true);
> + }
> +
> return ret;
> }
>
> --
> 2.18.0
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
