[Intel-xe] [PATCH] drm/xe: Fix lockdep warning in xe_force_wake calls

[Aravind Iddamsetty]

On 11/24/23 12:49, Ville Syrjälä wrote:
> On Fri, Nov 24, 2023 at 12:14:08PM +0530, Aravind Iddamsetty wrote:
>> Introduce atomic version for xe_force_wake calls which uses spin_lock
>> while the non atomic version uses spin_lock_irq
>>
>> Fix for below:
>> [13994.811263] ========================================================
>> [13994.811295] WARNING: possible irq lock inversion dependency detected
>> [13994.811326] 6.6.0-rc3-xe #2 Tainted: G     U
>> [13994.811358] --------------------------------------------------------
>> [13994.811388] swapper/0/0 just changed the state of lock:
>> [13994.811416] ffff895c7e044db8 (&cpuctx_lock){-...}-{2:2}, at:
>> __perf_event_read+0xb7/0x3a0
>> [13994.811494] but this lock took another, HARDIRQ-unsafe lock in the
>> past:
>> [13994.811528]  (&fw->lock){+.+.}-{2:2}
>> [13994.811544]
>>
>>                and interrupts could create inverse lock ordering between
>> them.
>>
>> [13994.811606]
>>                other info that might help us debug this:
>> [13994.811636]  Possible interrupt unsafe locking scenario:
>>
>> [13994.811667]        CPU0                    CPU1
>> [13994.811691]        ----                    ----
>> [13994.811715]   lock(&fw->lock);
>> [13994.811744]                                local_irq_disable();
>> [13994.811773]                                lock(&cpuctx_lock);
>> [13994.811810]                                lock(&fw->lock);
>> [13994.811846]   <Interrupt>
>> [13994.811865]     lock(&cpuctx_lock);
>> [13994.811895]
>>                 *** DEADLOCK ***
>>
>> v2: Use spin_lock in atomic context and spin_lock_irq in a non atomic
>> context (Matthew Brost)
> No idea what this "atomic context" means, but looks like
> you just want to use spin_lock_irqsave() & co.
atomic context: where sleeping is not allowed. Well that is what I had in
v1 and Matt suggested we should explicitly know from where we are calling
force wake and depending on it use spin_lock or spin_lock_irq versions.
>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> Cc: Anshuman Gupta <anshuman.gupta at intel.com>
>> Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
>> Signed-off-by: Aravind Iddamsetty <aravind.iddamsetty at linux.intel.com>
>> ---
>>  drivers/gpu/drm/xe/xe_force_wake.c | 62 +++++++++++++++++++++++++++++-
>>  drivers/gpu/drm/xe/xe_force_wake.h |  4 ++
>>  drivers/gpu/drm/xe/xe_pmu.c        |  4 +-
>>  3 files changed, 66 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_force_wake.c b/drivers/gpu/drm/xe/xe_force_wake.c
>> index 32d6c4dd2807..1693097f72d3 100644
>> --- a/drivers/gpu/drm/xe/xe_force_wake.c
>> +++ b/drivers/gpu/drm/xe/xe_force_wake.c
>> @@ -147,7 +147,7 @@ int xe_force_wake_get(struct xe_force_wake *fw,
>>  	enum xe_force_wake_domains tmp, woken = 0;
>>  	int ret, ret2 = 0;
>>  
>> -	spin_lock(&fw->lock);
>> +	spin_lock_irq(&fw->lock);
>>  	for_each_fw_domain_masked(domain, domains, fw, tmp) {
>>  		if (!domain->ref++) {
>>  			woken |= BIT(domain->id);
>> @@ -162,7 +162,7 @@ int xe_force_wake_get(struct xe_force_wake *fw,
>>  				   domain->id, ret);
>>  	}
>>  	fw->awake_domains |= woken;
>> -	spin_unlock(&fw->lock);
>> +	spin_unlock_irq(&fw->lock);
>>  
>>  	return ret2;
>>  }
>> @@ -176,6 +176,64 @@ int xe_force_wake_put(struct xe_force_wake *fw,
>>  	enum xe_force_wake_domains tmp, sleep = 0;
>>  	int ret, ret2 = 0;
>>  
>> +	spin_lock_irq(&fw->lock);
>> +	for_each_fw_domain_masked(domain, domains, fw, tmp) {
>> +		if (!--domain->ref) {
>> +			sleep |= BIT(domain->id);
>> +			domain_sleep(gt, domain);
>> +		}
>> +	}
>> +	for_each_fw_domain_masked(domain, sleep, fw, tmp) {
>> +		ret = domain_sleep_wait(gt, domain);
> Why on earth are we waiting here?
>
> Why is this all this stuff called "sleep something"?
to my knowledge the HW can take sometime to ack the forcewake request
that is why we have a wait, regarding the naming it was existing from before
may be Matt can answer that.


Thanks,
Aravind.
>