On 20/11/2020 14:26, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2020-11-20 09:56:35)
>> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>>
>> Guc->mmio_msg is set under the guc->irq_lock in guc_get_mmio_msg so it
>> should be consumed under the same lock from guc_handle_mmio_msg.
>>
>> I am not sure if the overall flow here makes complete sense but at least
>> the correct lock is now used.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
>> ---
>> drivers/gpu/drm/i915/gt/uc/intel_uc.c | 16 ++++++----------
>> 1 file changed, 6 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
>> index 4e6070e95fe9..220626c3ad81 100644
>> --- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c
>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
>> @@ -175,19 +175,15 @@ static void guc_get_mmio_msg(struct intel_guc *guc)
>>
>> static void guc_handle_mmio_msg(struct intel_guc *guc)
>> {
>> - struct drm_i915_private *i915 = guc_to_gt(guc)->i915;
>> -
>> /* we need communication to be enabled to reply to GuC */
>> GEM_BUG_ON(!guc_communication_enabled(guc));
>>
>> - if (!guc->mmio_msg)
>> - return;
>> -
>> - spin_lock_irq(&i915->irq_lock);
>> - intel_guc_to_host_process_recv_msg(guc, &guc->mmio_msg, 1);
>> - spin_unlock_irq(&i915->irq_lock);
>> -
>> - guc->mmio_msg = 0;
>> + spin_lock_irq(&guc->irq_lock);
>> + if (guc->mmio_msg) {
>> + intel_guc_to_host_process_recv_msg(guc, &guc->mmio_msg, 1);
>> + guc->mmio_msg = 0;
>> + }
>> + spin_unlock_irq(&guc->irq_lock);
>
> Based on just looking at mmio_msg, the locking should be guc->irq_lock, and
> guc->mmio_msg = 0 should be pulled under the lock.
>
> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Thanks, the thing which made me say that I am not sure it completely makes sense is that the mmio_msg appears to only be used from guc_enable_communication and
guc_disable_communication, which I would assume should be mutually exclusive by itself already. So I was not sure what value is there in the locking around mmio_msg access.
And even in guc_enable_communication we have a sequence of:
guc_get_mmio_msg(guc);
guc_handle_mmio_msg(guc);
Which expands to:
static void guc_get_mmio_msg(struct intel_guc *guc)
{
u32 val;
spin_lock_irq(&guc->irq_lock);
val = intel_uncore_read(guc_to_gt(guc)->uncore, SOFT_SCRATCH(15));
guc->mmio_msg |= val & guc->msg_enabled_mask;
/*
* clear all events, including the ones we're not currently servicing,
* to make sure we don't try to process a stale message if we enable
* handling of more events later.
*/
guc_clear_mmio_msg(guc);
spin_unlock_irq(&guc->irq_lock);
}
static void guc_handle_mmio_msg(struct intel_guc *guc)
{
/* we need communication to be enabled to reply to GuC */
GEM_BUG_ON(!guc_communication_enabled(guc));
spin_lock_irq(&guc->irq_lock);
if (guc->mmio_msg) {
intel_guc_to_host_process_recv_msg(guc, &guc->mmio_msg, 1);
guc->mmio_msg = 0;
}
spin_unlock_irq(&guc->irq_lock);
}
So it seems a bit pointless. Nevertheless I only wanted to remove usage of i915->irq_lock.
Regards,
Tvrtko
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