On 20 July 2017 at 12:27, Alex Xie <AlexBin.Xie at amd.com> wrote:
> In RCU read-side critical sections, blocking or sleeping is prohibited.
>
Seems to work here.
Tested-by: Dave Airlie <airlied at redhat.com>
> 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 {
> + rcu_read_unlock();
> result = NULL;
> + }
> }
> - rcu_read_unlock();
>
> return result;
> }
> --
> 2.7.4
>
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