On Tue, Sep 01, 2020 at 04:28:19AM +0800, Mathieu Poirier wrote:
On Fri, Aug 28, 2020 at 11:18:18AM +0800, Tingwei Zhang wrote:
On Fri, Aug 28, 2020 at 02:12:53AM +0800, Mathieu Poirier wrote:
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?
I cut some CPU registers' value since it's too long and not relevant. The Call trace is full.
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?
Most of them is correct. The only difference is CPUx is power on when cti_enable_hw() is called. Otherwise it will goto cti_state_unchanged: and won't call cti_enable_hw_smp_call(). cti_cpu_pm_notify() is called when CPUx tries to suspend instead of resume.
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'm not sure I understand this correctly. Let me clarify it a little
bit.
It's a deadlock since cti_enable_hw() holds the spinlock and calls cti_enable_hw_smp_call() from CPUx to enable CTI associated to CPUy. It waits for cti_enable_hw_smp_call() to return. IPI is sent to CPUy while CPUy is in cti_cpu_pm_notify() and waits for spinlock. In this patch, I remove cti_enable_hw_smp_call() and write CTI CPU directly on CPUx. It won't wait for CPUy and release spinlock after program registers of CTI. After cti_enable_hw() releases spinlock, cti_cpu_pm_notify() will continue to run. Since spinlock is held and config->hw_powered is true, we don't need to worry about CPUy power down when we program CTI on
CPUx.
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.
After cti_enable_hw() releases the lock, it's possible that CPU is
offline
by user, cti_enable_hw_smp_call() will fail in this case.
I took another look at your solution and you are correct, CPUy won't lock but rather spin waiting for cti_enable_hw() to finish on CPUx. To make sure CPUx is not interrupted while executing cti_enable_hw() I suggest to use spin_lock_irq().
Thanks, Mathieu
Sure. I've sent v2 according to your comments.
I have applied the other two patches in this set so no need to send
them
again.
Thanks, Tingwei
Thanks, Mathieu
Fixes: 6a0953ce7de9 ("coresight: cti: Add CPU idle pm notifer to CTI
devices")
Signed-off-by: Tingwei Zhang tingwei@codeaurora.org
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); -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
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