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

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

[Alex Xie]

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@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@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 {
+			rcu_read_unlock();
 			result = NULL;
+		}
+	}
+	else {
+		rcu_read_unlock();
 	}
-	rcu_read_unlock();
 
 	return result;
 }
-- 
2.7.4

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

[zhoucm1]

one small nit pick, with that fix, Reviewed-by: Chunming Zhou 
<david1.zhou@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@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@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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Re: [PATCH] drm/amdgpu: Fix blocking in RCU critical section(v2)

[Christian König]

Yeah, with the coding style fixed Reviewed-by: Christian König 
<christian.koenig@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@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@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@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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> amd-gfx@lists.freedesktop.org
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Re: [PATCH] drm/amdgpu: Fix blocking in RCU critical section(v2)

[Emil Velikov]

Hi Alex,

On 20 July 2017 at 03:46, Alex Xie <AlexBin.Xie@amd.com> wrote:
> --- 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 {
> +                       rcu_read_unlock();
>                         result = NULL;
> +               }
> +       }
> +       else {
> +               rcu_read_unlock();
>         }
> -       rcu_read_unlock();
>
>         return result;
A drive-by suggestion - feel free to ignore.

The "return early" approach seems great IMHO. The code will be
shorter, indentation - less, no {}/else to track plus overall it seems
clearer.
Namely:

   result = idr_find(&fpriv->bo_list_handles, id);

   if (!result || !kref_get_unless_zero(&result->refcount)) {
         rcu_read_unlock();
         return NULL;
   }

   rcu_read_unlock();
   mutex_lock(&result->lock);
   return result;
}

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

[axie]

Hi Emil,

Sorry for late reply. I was so busy last week and this week.

Your logic looks correct, smarter and shorter. I feel relatively more 
difficult to understand the logic, with two "!" and one "||" in the same 
if statement.

Thanks for the advice always.

On 2017-07-20 02:29 PM, Emil Velikov wrote:
> Hi Alex,
>
> On 20 July 2017 at 03:46, Alex Xie <AlexBin.Xie@amd.com> wrote:
>> --- 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 {
>> +                       rcu_read_unlock();
>>                          result = NULL;
>> +               }
>> +       }
>> +       else {
>> +               rcu_read_unlock();
>>          }
>> -       rcu_read_unlock();
>>
>>          return result;
> A drive-by suggestion - feel free to ignore.
>
> The "return early" approach seems great IMHO. The code will be
> shorter, indentation - less, no {}/else to track plus overall it seems
> clearer.
> Namely:
>
>     result = idr_find(&fpriv->bo_list_handles, id);
>
>     if (!result || !kref_get_unless_zero(&result->refcount)) {
>           rcu_read_unlock();
>           return NULL;
>     }
>
>     rcu_read_unlock();
>     mutex_lock(&result->lock);
>     return result;
> }
>
> HTH
> Emil

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