On 16 June 2017 at 23:08, Alex Xie <AlexBin.Xie at amd.com> wrote:
> In original function amdgpu_bo_list_get, the waiting
> for result->lock can be quite long while mutex
> bo_list_lock was holding. It can make other tasks
> waiting for bo_list_lock for long period.
>
> Secondly, this patch allows several tasks(readers of idr)
> to proceed at the same time.
>
> v2: use rcu and kref (Dave Airlie and Christian König)
> v3: update v1 commit message (Michel Dänzer)
Got this, I'm guessing due to this patch.
Dave.
[ 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.h | 2 ++
> drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 40 ++++++++++++++++++++---------
> 2 files changed, 30 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> index 063fc73..e9b3981 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> @@ -871,6 +871,8 @@ struct amdgpu_fpriv {
>
> struct amdgpu_bo_list {
> struct mutex lock;
> + struct rcu_head rhead;
> + struct kref refcount;
> struct amdgpu_bo *gds_obj;
> struct amdgpu_bo *gws_obj;
> struct amdgpu_bo *oa_obj;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> index 5af956f..efa6903 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> @@ -41,6 +41,20 @@ static int amdgpu_bo_list_set(struct amdgpu_device *adev,
> struct drm_amdgpu_bo_list_entry *info,
> unsigned num_entries);
>
> +static void amdgpu_bo_list_release_rcu(struct kref *ref)
> +{
> + unsigned i;
> + struct amdgpu_bo_list *list = container_of(ref, struct amdgpu_bo_list,
> + refcount);
> +
> + for (i = 0; i < list->num_entries; ++i)
> + amdgpu_bo_unref(&list->array[i].robj);
> +
> + mutex_destroy(&list->lock);
> + drm_free_large(list->array);
> + kfree_rcu(list, rhead);
> +}
> +
> static int amdgpu_bo_list_create(struct amdgpu_device *adev,
> struct drm_file *filp,
> struct drm_amdgpu_bo_list_entry *info,
> @@ -57,7 +71,7 @@ static int amdgpu_bo_list_create(struct amdgpu_device *adev,
>
> /* initialize bo list*/
> mutex_init(&list->lock);
> -
> + kref_init(&list->refcount);
> r = amdgpu_bo_list_set(adev, filp, list, info, num_entries);
> if (r) {
> kfree(list);
> @@ -83,14 +97,9 @@ static void amdgpu_bo_list_destroy(struct amdgpu_fpriv *fpriv, int id)
>
> mutex_lock(&fpriv->bo_list_lock);
> list = idr_remove(&fpriv->bo_list_handles, id);
> - if (list) {
> - /* Another user may have a reference to this list still */
> - mutex_lock(&list->lock);
> - mutex_unlock(&list->lock);
> - amdgpu_bo_list_free(list);
> - }
> -
> mutex_unlock(&fpriv->bo_list_lock);
> + if (list)
> + kref_put(&list->refcount, amdgpu_bo_list_release_rcu);
> }
>
> static int amdgpu_bo_list_set(struct amdgpu_device *adev,
> @@ -185,11 +194,17 @@ amdgpu_bo_list_get(struct amdgpu_fpriv *fpriv, int id)
> {
> struct amdgpu_bo_list *result;
>
> - mutex_lock(&fpriv->bo_list_lock);
> + rcu_read_lock();
> result = idr_find(&fpriv->bo_list_handles, id);
> - if (result)
> - mutex_lock(&result->lock);
> - mutex_unlock(&fpriv->bo_list_lock);
> +
> + if (result) {
> + if (kref_get_unless_zero(&result->refcount))
> + mutex_lock(&result->lock);
> + else
> + result = NULL;
> + }
> + rcu_read_unlock();
> +
> return result;
> }
>
> @@ -227,6 +242,7 @@ void amdgpu_bo_list_get_list(struct amdgpu_bo_list *list,
> void amdgpu_bo_list_put(struct amdgpu_bo_list *list)
> {
> mutex_unlock(&list->lock);
> + kref_put(&list->refcount, amdgpu_bo_list_release_rcu);
> }
>
> void amdgpu_bo_list_free(struct amdgpu_bo_list *list)
> --
> 2.7.4
>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
