Re: [PATCH 6/8] drm/i915: add struct_mutex WARNs to i915_gem_stolen.c

From: Paulo Zanoni <przanoni@gmail.com>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	Paulo Zanoni <przanoni@gmail.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Paulo Zanoni <paulo.r.zanoni@intel.com>
Subject: Re: [PATCH 6/8] drm/i915: add struct_mutex WARNs to i915_gem_stolen.c
Date: Tue, 30 Jun 2015 11:26:11 -0300	[thread overview]
Message-ID: <CA+gsUGRy5J9yapJf4fAwtWmb7waFWinkCmrY6fVG9wB6hx5T2Q@mail.gmail.com> (raw)
In-Reply-To: <20150630141533.GZ1381@nuc-i3427.alporthouse.com>

2015-06-30 11:15 GMT-03:00 Chris Wilson <chris@chris-wilson.co.uk>:
> On Tue, Jun 30, 2015 at 10:53:10AM -0300, Paulo Zanoni wrote:
>> From: Paulo Zanoni <paulo.r.zanoni@intel.com>
>>
>> Let's make sure the future Paulos don't forget that we need
>> struct_mutex when touching dev_priv->mm.stolen.
>>
>> Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_gem_stolen.c | 13 +++++++++++++
>>  1 file changed, 13 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
>> index 793bcba..cac1bce 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
>> @@ -160,6 +160,8 @@ static int find_compression_threshold(struct drm_device *dev,
>>       int compression_threshold = 1;
>>       int ret;
>>
>> +     WARN_ON(!mutex_is_locked(&dev->struct_mutex));
>
> I'm not a huge fan of vague mutex warnings that don't even check the owner.
> I'm espcially not a fan of adding a WARN and not handling the error.

But then, what exactly is your proposal? What would you like to see here?

We can discard this patch if you want. But I hope you're not
advocating for lockdep_assert_held(), because if I switch to lockdep,
then Daniel is going to deny it again. Also, this type of WARN_ON is a
common pattern on our codebase...

> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre

-- 
Paulo Zanoni
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