[PATCH] drm/amdgpu: Fix blocking in RCU critical section(v2)

[Christian König]

Yeah, with the coding style fixed Reviewed-by: Christian König 
<christian.koenig at amd.com> as well.

Christian.

Am 20.07.2017 um 05:01 schrieb zhoucm1:
> one small nit pick, with that fix, Reviewed-by: Chunming Zhou 
> <david1.zhou at amd.com>
>
> On 2017年07月20日 10:46, Alex Xie wrote:
>> In RCU read-side critical sections, blocking or sleeping is prohibited.
>>
>> v2: Unlock RCU for the code path where result==NULL. (David Zhou)
>>      Update subject
>>
>> Tested-by and reported by: Dave Airlie <airlied at redhat.com>
>>
>> [  141.965723] =============================
>> [  141.965724] WARNING: suspicious RCU usage
>> [  141.965726] 4.12.0-rc7 #221 Not tainted
>> [  141.965727] -----------------------------
>> [  141.965728] 
>> /home/airlied/devel/kernel/linux-2.6/include/linux/rcupdate.h:531
>> Illegal context switch in RCU read-side critical section!
>> [  141.965730]
>>                 other info that might help us debug this:
>>
>> [  141.965731]
>>                 rcu_scheduler_active = 2, debug_locks = 0
>> [  141.965732] 1 lock held by amdgpu_cs:0/1332:
>> [  141.965733]  #0:  (rcu_read_lock){......}, at: [<ffffffffa01a0d07>]
>> amdgpu_bo_list_get+0x0/0x109 [amdgpu]
>> [  141.965774]
>>                 stack backtrace:
>> [  141.965776] CPU: 6 PID: 1332 Comm: amdgpu_cs:0 Not tainted 
>> 4.12.0-rc7 #221
>> [  141.965777] Hardware name: To be filled by O.E.M. To be filled by
>> O.E.M./M5A97 R2.0, BIOS 2603 06/26/2015
>> [  141.965778] Call Trace:
>> [  141.965782]  dump_stack+0x68/0x92
>> [  141.965785]  lockdep_rcu_suspicious+0xf7/0x100
>> [  141.965788]  ___might_sleep+0x56/0x1fc
>> [  141.965790]  __might_sleep+0x68/0x6f
>> [  141.965793]  __mutex_lock+0x4e/0x7b5
>> [  141.965817]  ? amdgpu_bo_list_get+0xa4/0x109 [amdgpu]
>> [  141.965820]  ? lock_acquire+0x125/0x1b9
>> [  141.965844]  ? amdgpu_bo_list_set+0x464/0x464 [amdgpu]
>> [  141.965846]  mutex_lock_nested+0x16/0x18
>> [  141.965848]  ? mutex_lock_nested+0x16/0x18
>> [  141.965872]  amdgpu_bo_list_get+0xa4/0x109 [amdgpu]
>> [  141.965895]  amdgpu_cs_ioctl+0x4a0/0x17dd [amdgpu]
>> [  141.965898]  ? radix_tree_node_alloc.constprop.11+0x77/0xab
>> [  141.965916]  drm_ioctl+0x264/0x393 [drm]
>> [  141.965939]  ? amdgpu_cs_find_mapping+0x83/0x83 [amdgpu]
>> [  141.965942]  ? trace_hardirqs_on_caller+0x16a/0x186
>>
>> Signed-off-by: Alex Xie <AlexBin.Xie at amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 12 +++++++++---
>>   1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
>> index dc87962..e5d61fe 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
>> @@ -198,12 +198,18 @@ amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, 
>> int id)
>>       result = idr_find(&fpriv->bo_list_handles, id);
>>         if (result) {
>> -        if (kref_get_unless_zero(&result->refcount))
>> +        if (kref_get_unless_zero(&result->refcount)) {
>> +            rcu_read_unlock();
>>               mutex_lock(&result->lock);
>> -        else
>> +        }
>> +        else {
> don't need another line, just like } else {
>> +            rcu_read_unlock();
>>               result = NULL;
>> +        }
>> +    }
>> +    else {
> don't need another line, just like } else {
>> +        rcu_read_unlock();
>>       }
>> -    rcu_read_unlock();
>>         return result;
>>   }
>
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