[PATCH] drm/amdgpu: Fix error RCU usage

[Deucher, Alexander]

> -----Original Message-----
> From: amd-gfx [mailto:amd-gfx-bounces at lists.freedesktop.org] On Behalf
> Of Alex Xie
> Sent: Wednesday, July 19, 2017 10:28 PM
> To: amd-gfx at lists.freedesktop.org
> Cc: Xie, AlexBin
> Subject: [PATCH] drm/amdgpu: Fix error RCU usage
> 
> In RCU read-side critical sections, blocking or sleeping is prohibited.
> 
> 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: [<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 | 9 ++++++---
>  1 file changed, 6 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..565ca90 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> @@ -198,12 +198,15 @@ 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 {

Coding style,  open paren should be on same line as else.  E.g.,
} else {

Alex

> +			rcu_read_unlock();
>  			result = NULL;
> +		}
>  	}
> -	rcu_read_unlock();
> 
>  	return result;
>  }
> --
> 2.7.4
> 
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