Re: [PATCH] drm/i915: Do not store the error pointer for a failed userptr registration

[Jani Nikula <jani.nikula@linux.intel.com>]

On Fri, 26 Sep 2014, Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> wrote:
> On 09/26/2014 10:31 AM, Chris Wilson wrote:
>> If we fail to create our mmu notification, we report the error back and
>> currently store the error inside the i915_mm_struct. This not only causes
>> subsequent registerations of the same mm to fail (an issue if the first
>> was interrupted by a signal and needed to be restarted) but also causes
>> us to eventually try and free the error pointer.
>>
>> [   73.419599] BUG: unable to handle kernel NULL pointer dereference at 000000000000004c
>> [   73.419831] IP: [<ffffffff8114af33>] mmu_notifier_unregister+0x23/0x130
>> [   73.420065] PGD 8650c067 PUD 870bb067 PMD 0
>> [   73.420319] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
>> [   73.420580] CPU: 0 PID: 42 Comm: kworker/0:1 Tainted: G        W      3.17.0-rc6+ #1561
>> [   73.420837] Hardware name: Intel Corporation SandyBridge Platform/LosLunas CRB, BIOS ASNBCPT1.86C.0075.P00.1106281639 06/28/2011
>> [   73.421405] Workqueue: events __i915_mm_struct_free__worker
>> [   73.421724] task: ffff880088a81220 ti: ffff880088168000 task.ti: ffff880088168000
>> [   73.422051] RIP: 0010:[<ffffffff8114af33>]  [<ffffffff8114af33>] mmu_notifier_unregister+0x23/0x130
>> [   73.422410] RSP: 0018:ffff88008816bd50  EFLAGS: 00010286
>> [   73.422765] RAX: 0000000000000003 RBX: ffff880086485400 RCX: 0000000000000000
>> [   73.423137] RDX: ffff88016d80ee90 RSI: ffff880086485400 RDI: 0000000000000044
>> [   73.423513] RBP: ffff88008816bd70 R08: 0000000000000001 R09: 0000000000000000
>> [   73.423895] R10: 0000000000000320 R11: 0000000000000001 R12: 0000000000000044
>> [   73.424282] R13: ffff880166e5f008 R14: ffff88016d815200 R15: ffff880166e5f040
>> [   73.424682] FS:  0000000000000000(0000) GS:ffff88016d800000(0000) knlGS:0000000000000000
>> [   73.425099] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [   73.425537] CR2: 000000000000004c CR3: 0000000087f5f000 CR4: 00000000000407f0
>> [   73.426157] Stack:
>> [   73.426597]  ffff880088a81248 ffff880166e5f038 fffffffffffffffc ffff880166e5f008
>> [   73.427096]  ffff88008816bd98 ffffffff814a75f2 ffff880166e5f038 ffff8800880f8a28
>> [   73.427603]  ffff88016d812ac0 ffff88008816be00 ffffffff8106321a ffffffff810631af
>> [   73.428119] Call Trace:
>> [   73.428606]  [<ffffffff814a75f2>] __i915_mm_struct_free__worker+0x42/0x80
>> [   73.429116]  [<ffffffff8106321a>] process_one_work+0x1ba/0x610
>> [   73.429632]  [<ffffffff810631af>] ? process_one_work+0x14f/0x610
>> [   73.430153]  [<ffffffff810636db>] worker_thread+0x6b/0x4a0
>> [   73.430671]  [<ffffffff8108d67d>] ? trace_hardirqs_on+0xd/0x10
>> [   73.431501]  [<ffffffff81063670>] ? process_one_work+0x610/0x610
>> [   73.432030]  [<ffffffff8106a206>] kthread+0xf6/0x110
>> [   73.432561]  [<ffffffff8106a110>] ? __kthread_parkme+0x80/0x80
>> [   73.433100]  [<ffffffff8169c22c>] ret_from_fork+0x7c/0xb0
>> [   73.433644]  [<ffffffff8106a110>] ? __kthread_parkme+0x80/0x80
>> [   73.434194] Code: 0f 1f 84 00 00 00 00 00 66 66 66 66 90 8b 46 4c 85 c0 0f 8e 10 01 00 00 55 48 89 e5 41 55 41 54 53 48 89 f3 49 89 fc 48 83 ec 08 <48> 83 7f 08 00 0f 84 b1 00 00 00 48 c7 c7 40 e6 ac 82 e8 26 65
>> [   73.435942] RIP  [<ffffffff8114af33>] mmu_notifier_unregister+0x23/0x130
>> [   73.437017]  RSP <ffff88008816bd50>
>> [   73.437704] CR2: 000000000000004c
>>
>> Fixes regression from commit ad46cb533d586fdb256855437af876617c6cf609
>> Author: Chris Wilson <chris@chris-wilson.co.uk>
>> Date:   Thu Aug 7 14:20:40 2014 +0100
>>
>>      drm/i915: Prevent recursive deadlock on releasing a busy userptr
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84207
>> Testcase: igt/gem_render_copy_redux
>> Testcase: igt/gem_userptr_blits/create-destroy-sync
>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Jacek Danecki <jacek.danecki@intel.com>
>> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com>
>> Cc: Jacek Danecki <jacek.danecki@intel.com>
>> Cc: "Ursulin, Tvrtko" <tvrtko.ursulin@intel.com>
>> Cc: stable@vger.kernel.org
>> ---
>>   drivers/gpu/drm/i915/i915_gem_userptr.c | 24 ++++++++++++++++--------
>>   1 file changed, 16 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
>> index 903a875..ecd5c84 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
>> @@ -293,15 +293,23 @@ i915_gem_userptr_release__mmu_notifier(struct drm_i915_gem_object *obj)
>>   static struct i915_mmu_notifier *
>>   i915_mmu_notifier_find(struct i915_mm_struct *mm)
>>   {
>> -	if (mm->mn == NULL) {
>> -		down_write(&mm->mm->mmap_sem);
>> -		mutex_lock(&to_i915(mm->dev)->mm_lock);
>> -		if (mm->mn == NULL)
>> -			mm->mn = i915_mmu_notifier_create(mm->mm);
>> -		mutex_unlock(&to_i915(mm->dev)->mm_lock);
>> -		up_write(&mm->mm->mmap_sem);
>> +	struct i915_mmu_notifier *mn = mm->mn;
>> +
>> +	mn = mm->mn;
>> +	if (mn)
>> +		return mn;
>> +
>> +	down_write(&mm->mm->mmap_sem);
>> +	mutex_lock(&to_i915(mm->dev)->mm_lock);
>> +	if ((mn = mm->mn) == NULL) {
>> +		mn = i915_mmu_notifier_create(mm->mm);
>> +		if (!IS_ERR(mn))
>> +			mm->mn = mn;
>>   	}
>> -	return mm->mn;
>> +	mutex_unlock(&to_i915(mm->dev)->mm_lock);
>> +	up_write(&mm->mm->mmap_sem);
>> +
>> +	return mn;
>>   }
>>
>>   static int
>>
>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Pushed to drm-intel-fixes, thanks for the patch and review.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center