Re: [Intel-gfx] [PATCH v3 04/63] drm/i915: Pin timeline map after first timeline pin, v3.

From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: "Thomas Hellström (Intel)" <thomas_os@shipmail.org>,
	intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH v3 04/63] drm/i915: Pin timeline map after first timeline pin, v3.
Date: Tue, 27 Oct 2020 15:31:01 +0100	[thread overview]
Message-ID: <89f87f2f-a941-0769-4765-0b659b357703@linux.intel.com> (raw)
In-Reply-To: <8677ec74-b31e-05c9-2cdf-514fd11462e4@shipmail.org>

Op 27-10-2020 om 12:03 schreef Thomas Hellström (Intel):
>
> On 10/15/20 1:25 PM, Maarten Lankhorst wrote:
>> We're starting to require the reservation lock for pinning,
>> so wait until we have that.
>>
>> Update the selftests to handle this correctly, and ensure pin is
>> called in live_hwsp_rollover_user() and mock_hwsp_freelist().
>>
>> Changes since v1:
>> - Fix NULL + XX arithmatic, use casts. (kbuild)
>> Changes since v2:
>> - Clear entire cacheline when pinning.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Reported-by: kernel test robot <lkp@intel.com>
> ...
>> @@ -150,6 +161,12 @@ int intel_timeline_pin(struct intel_timeline *tl, struct i915_gem_ww_ctx *ww)
>>       if (atomic_add_unless(&tl->pin_count, 1, 0))
>>           return 0;
>>   +    if (!tl->hwsp_map) {
>> +        err = intel_timeline_pin_map(tl);
>> +        if (err)
>> +            return err;
>> +    }
>> +
>
> On subsequent errors or if somebody beats us to the 0->1 transition, we need to unpin_map to avoid leaking pins.

No? tl->hwsp_map can stay set. We hold a lock to tl->hwsp_ggtt to prevent any races. :)

~Maarten

>>       err = i915_ggtt_pin(tl->hwsp_ggtt, ww, 0, PIN_HIGH);
>>       if (err)
>>           return err;
>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_timeline.h b/drivers/gpu/drm/i915/gt/intel_timeline.h
>> index 9882cd911d8e..1cfdc4679b62 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_timeline.h
>> +++ b/drivers/gpu/drm/i915/gt/intel_timeline.h
>> @@ -106,4 +106,6 @@ int intel_timeline_read_hwsp(struct i915_request *from,
>>   void intel_gt_init_timelines(struct intel_gt *gt);
>>   void intel_gt_fini_timelines(struct intel_gt *gt);
>>   +I915_SELFTEST_DECLARE(int intel_timeline_pin_map(struct intel_timeline *tl));
>> +
>>   #endif
>> diff --git a/drivers/gpu/drm/i915/gt/mock_engine.c b/drivers/gpu/drm/i915/gt/mock_engine.c
>> index 2f830017c51d..effbac877eec 100644
>> --- a/drivers/gpu/drm/i915/gt/mock_engine.c
>> +++ b/drivers/gpu/drm/i915/gt/mock_engine.c
>> @@ -32,9 +32,20 @@
>>   #include "mock_engine.h"
>>   #include "selftests/mock_request.h"
>>   -static void mock_timeline_pin(struct intel_timeline *tl)
>> +static int mock_timeline_pin(struct intel_timeline *tl)
>>   {
>> +    int err;
>> +
>> +    if (WARN_ON(!i915_gem_object_trylock(tl->hwsp_ggtt->obj)))
>> +        return -EBUSY;
>
> I think we should either annotate this properly as an isolated lock, or allow a silent -EBUSY. 

This is done in a controlled selftest where we mock the entire i915 device, so normally this can't happen. :)

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