| Message ID | 20220725043000.5086-1-peter.wang@mediatek.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] ufs: core: fix lockdep warning of clk_scaling_lock | expand |
On 7/24/22 21:30, peter.wang@mediatek.com wrote: > From: Peter Wang <peter.wang@mediatek.com> > > 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. Since this is a bug fix, please add a Fixes: tag. > 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); > + > return ret; > } Can the above patch can have the following unwanted effect? * ufshcd_devfreq_scale() calls ufshcd_clock_scaling_unprepare(). * Clock scaling to a lower frequency happens. * ufshcd_wb_toggle() enables the write booster. Shouldn't the above ufshcd_wb_toggle() call be surrounded by down_read() and up_read() calls in addition to a check whether the WriteBooster really should be enabled instead of using 'scale_up'? Thanks, Bart.
Hi Bart, On 7/26/22 12:56 AM, Bart Van Assche wrote: > On 7/24/22 21:30, peter.wang@mediatek.com wrote: >> From: Peter Wang <peter.wang@mediatek.com> >> >> 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. > > Since this is a bug fix, please add a Fixes: tag. Will add Fixes: tag in next version. > >> 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); >> + >> return ret; >> } > > Can the above patch can have the following unwanted effect? > * ufshcd_devfreq_scale() calls ufshcd_clock_scaling_unprepare(). > * Clock scaling to a lower frequency happens. > * ufshcd_wb_toggle() enables the write booster. > > Shouldn't the above ufshcd_wb_toggle() call be surrounded by > down_read() and up_read() calls in addition to a check whether the > WriteBooster really should be enabled instead of using 'scale_up'? > > Thanks, > > Bart. > > You means ufshcd_devfreq_scale may have racing in two thread, right? Then yes, it may have this unwanted effect in this condition. But ufshcd_wb_toggle should not hold clk_scaling_lock, or the deadlock may happen. I will change this patch to protect ufshcd_devfreq_scale racing and ufshcd_wb_toggle in next version. Thanks. Peter
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c index c7b337480e3e..209089bd8085 100644 --- a/drivers/ufs/core/ufshcd.c +++ b/drivers/ufs/core/ufshcd.c @@ -1249,12 +1249,10 @@ 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 +1269,7 @@ 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 +1298,15 @@ 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); + 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); + return ret; }