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

2017-07-26 Thread 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  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(>bo_list_handles, id);

 if (result) {
-   if (kref_get_unless_zero(>refcount))
+   if (kref_get_unless_zero(>refcount)) {
+   rcu_read_unlock();
 mutex_lock(>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(>bo_list_handles, id);

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

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

HTH
Emil


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

2017-07-20 Thread Emil Velikov 
Hi Alex,

On 20 July 2017 at 03:46, Alex Xie  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(>bo_list_handles, id);
>
> if (result) {
> -   if (kref_get_unless_zero(>refcount))
> +   if (kref_get_unless_zero(>refcount)) {
> +   rcu_read_unlock();
> mutex_lock(>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(>bo_list_handles, id);

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

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

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

2017-07-20 Thread Christian König 
Yeah, with the coding style fixed Reviewed-by: Christian König 
 as well.


Christian.

Am 20.07.2017 um 05:01 schrieb zhoucm1:
one small nit pick, with that fix, Reviewed-by: Chunming Zhou 



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 

[  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: []
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 
---
  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(>bo_list_handles, id);
if (result) {
-if (kref_get_unless_zero(>refcount))
+if (kref_get_unless_zero(>refcount)) {
+rcu_read_unlock();
  mutex_lock(>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)

2017-07-19 Thread zhoucm1 
one small nit pick, with that fix, Reviewed-by: Chunming Zhou 



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 

[  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: []
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 
---
  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(>bo_list_handles, id);
  
  	if (result) {

-   if (kref_get_unless_zero(>refcount))
+   if (kref_get_unless_zero(>refcount)) {
+   rcu_read_unlock();
mutex_lock(>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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[PATCH] drm/amdgpu: Fix blocking in RCU critical section(v2)

2017-07-19 Thread 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 

[  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: []
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 
---
 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(>bo_list_handles, id);
 
if (result) {
-   if (kref_get_unless_zero(>refcount))
+   if (kref_get_unless_zero(>refcount)) {
+   rcu_read_unlock();
mutex_lock(>lock);
-   else
+   }
+   else {
+   rcu_read_unlock();
result = NULL;
+   }
+   }
+   else {
+   rcu_read_unlock();
}
-   rcu_read_unlock();
 
return result;
 }
-- 
2.7.4

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