Re: [PATCH] coresight: cti: write regsiters directly in cti_enable_hw()

[Mathieu Poirier]

Hi Tingwei,

On Tue, Aug 18, 2020 at 07:10:57PM +0800, Tingwei Zhang wrote:
> Deadlock as below is triggered by one CPU holds drvdata->spinlock
> and calls cti_enable_hw(). Smp_call_function_single() is called
> in cti_enable_hw() and tries to let another CPU write CTI registers.
> That CPU is trying to get drvdata->spinlock in cti_cpu_pm_notify()
> and doesn't response to IPI from smp_call_function_single().
> 
> [  988.335937] CPU: 6 PID: 10258 Comm: sh Tainted: G        W    L
> 5.8.0-rc6-mainline-16783-gc38daa79b26b-dirty #1
> [  988.346364] Hardware name: Thundercomm Dragonboard 845c (DT)
> [  988.352073] pstate: 20400005 (nzCv daif +PAN -UAO BTYPE=--)
> [  988.357689] pc : smp_call_function_single+0x158/0x1b8
> [  988.362782] lr : smp_call_function_single+0x124/0x1b8
> ...
> [  988.451638] Call trace:
> [  988.454119]  smp_call_function_single+0x158/0x1b8
> [  988.458866]  cti_enable+0xb4/0xf8 [coresight_cti]
> [  988.463618]  coresight_control_assoc_ectdev+0x6c/0x128 [coresight]
> [  988.469855]  coresight_enable+0x1f0/0x364 [coresight]
> [  988.474957]  enable_source_store+0x5c/0x9c [coresight]
> [  988.480140]  dev_attr_store+0x14/0x28
> [  988.483839]  sysfs_kf_write+0x38/0x4c
> [  988.487532]  kernfs_fop_write+0x1c0/0x2b0
> [  988.491585]  vfs_write+0xfc/0x300
> [  988.494931]  ksys_write+0x78/0xe0
> [  988.498283]  __arm64_sys_write+0x18/0x20
> [  988.502240]  el0_svc_common+0x98/0x160
> [  988.506024]  do_el0_svc+0x78/0x80
> [  988.509377]  el0_sync_handler+0xd4/0x270
> [  988.513337]  el0_sync+0x164/0x180
> 

Was this the full log or you did cut some of it?

> This change write CTI registers directly in cti_enable_hw().
> Config->hw_powered has been checked to be true with spinlock holded.
> CTI is powered and can be programmed until spinlock is released.
> 

>From your explanation above it seems that cti_enable_hw() was called from, say
CPUy, to enable the CTI associated to CPUx.  CTIx's drvdata->spinlock was taken
and smp_call_function_single() called right after.  That woke up CPUx and
cti_cpu_pm_notify() was executed on CPUx in interrupt context, trying to take
CTIx's drvdata->spinlock.  That hung CPUx and the kernel got angry.  Is my
assessment correct?

If so I don't think the fix suggested in this patch will work.  The same
condition will happen whenever cti_enable_hw() is called on a CPU to enable a
CTI that belongs to another CPU and that cti_cpu_pm_notify() is called on latter
CPU at the same time.

I think a better solution is to grab the lock in cti_enable_hw() and check the
value of ->ctidev.cpu.  If not a global CPU, i.e >= 0, then release the lock and
call smp_call_function_single().  In cti_enable_hw_smp_call() take the lock
again and move forward from there. 

I have applied the other two patches in this set so no need to send them again.

Thanks,
Mathieu

> Fixes: 6a0953ce7de9 ("coresight: cti: Add CPU idle pm notifer to CTI devices")
> Signed-off-by: Tingwei Zhang <tingwei@xxxxxxxxxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-cti.c | 17 +----------------
>  1 file changed, 1 insertion(+), 16 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-cti.c b/drivers/hwtracing/coresight/coresight-cti.c
> index 3ccc703dc940..869569eb8c7f 100644
> --- a/drivers/hwtracing/coresight/coresight-cti.c
> +++ b/drivers/hwtracing/coresight/coresight-cti.c
> @@ -86,13 +86,6 @@ void cti_write_all_hw_regs(struct cti_drvdata *drvdata)
>  	CS_LOCK(drvdata->base);
>  }
>  
> -static void cti_enable_hw_smp_call(void *info)
> -{
> -	struct cti_drvdata *drvdata = info;
> -
> -	cti_write_all_hw_regs(drvdata);
> -}
> -
>  /* write regs to hardware and enable */
>  static int cti_enable_hw(struct cti_drvdata *drvdata)
>  {
> @@ -112,15 +105,7 @@ static int cti_enable_hw(struct cti_drvdata *drvdata)
>  	if (rc)
>  		goto cti_err_not_enabled;
>  
> -	if (drvdata->ctidev.cpu >= 0) {
> -		rc = smp_call_function_single(drvdata->ctidev.cpu,
> -					      cti_enable_hw_smp_call,
> -					      drvdata, 1);
> -		if (rc)
> -			goto cti_err_not_enabled;
> -	} else {
> -		cti_write_all_hw_regs(drvdata);
> -	}
> +	cti_write_all_hw_regs(drvdata);
>  
>  	config->hw_enabled = true;
>  	atomic_inc(&drvdata->config.enable_req_count);
> -- 
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