[PATCH 1/2] drm/syncobj: Mark up the fence as an RCU protected pointer

[PATCH 1/2] drm/syncobj: Mark up the fence as an RCU protected pointer

[Chris Wilson]

We take advantage of that syncobj->fence is an RCU-protected pointer, and
so sparse complains that it is lacking annotation.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 include/drm/drm_syncobj.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
index c00fee539822..455660673259 100644
--- a/include/drm/drm_syncobj.h
+++ b/include/drm/drm_syncobj.h
@@ -49,7 +49,7 @@ struct drm_syncobj {
 	 * This field should not be used directly.  Use drm_syncobj_fence_get
 	 * and drm_syncobj_replace_fence instead.
 	 */
-	struct dma_fence *fence;
+	struct dma_fence __rcu *fence;
 	/**
 	 * @cb_list:
 	 * List of callbacks to call when the fence gets replaced
-- 
2.14.1

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[PATCH 2/2] dma-buf/fence: Sparse wants __rcu on the object itself

[Chris Wilson]

In order to silent sparse in dma_fence_get_rcu_safe(), we need to mark
the incoming fence object as being RCU protected and not the pointer to
the object.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 include/linux/dma-fence.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 171895072435..bad861f8f914 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -242,7 +242,7 @@ static inline struct dma_fence *dma_fence_get_rcu(struct dma_fence *fence)
  * The caller is required to hold the RCU read lock.
  */
 static inline struct dma_fence *
-dma_fence_get_rcu_safe(struct dma_fence * __rcu *fencep)
+dma_fence_get_rcu_safe(struct dma_fence __rcu **fencep)
 {
 	do {
 		struct dma_fence *fence;
-- 
2.14.1

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✓ Fi.CI.BAT: success for series starting with [1/2] drm/syncobj: Mark up the fence as an RCU protected pointer

[Patchwork]

== Series Details ==

Series: series starting with [1/2] drm/syncobj: Mark up the fence as an RCU protected pointer
URL   : https://patchwork.freedesktop.org/series/29700/
State : success

== Summary ==

Series 29700v1 series starting with [1/2] drm/syncobj: Mark up the fence as an RCU protected pointer
https://patchwork.freedesktop.org/api/1.0/series/29700/revisions/1/mbox/

Test kms_cursor_legacy:
        Subgroup basic-busy-flip-before-cursor-legacy:
                fail       -> PASS       (fi-snb-2600) fdo#100215
Test kms_flip:
        Subgroup basic-flip-vs-modeset:
                skip       -> PASS       (fi-skl-x1585l) fdo#101781
Test kms_pipe_crc_basic:
        Subgroup suspend-read-crc-pipe-b:
                dmesg-warn -> PASS       (fi-byt-n2820) fdo#101705

fdo#100215 https://bugs.freedesktop.org/show_bug.cgi?id=100215
fdo#101781 https://bugs.freedesktop.org/show_bug.cgi?id=101781
fdo#101705 https://bugs.freedesktop.org/show_bug.cgi?id=101705

fi-bdw-5557u     total:288  pass:268  dwarn:0   dfail:0   fail:0   skip:20  time:455s
fi-bdw-gvtdvm    total:288  pass:265  dwarn:0   dfail:0   fail:0   skip:23  time:443s
fi-blb-e6850     total:288  pass:224  dwarn:1   dfail:0   fail:0   skip:63  time:362s
fi-bsw-n3050     total:288  pass:243  dwarn:0   dfail:0   fail:0   skip:45  time:553s
fi-bwr-2160      total:288  pass:184  dwarn:0   dfail:0   fail:0   skip:104 time:253s
fi-bxt-j4205     total:288  pass:260  dwarn:0   dfail:0   fail:0   skip:28  time:526s
fi-byt-j1900     total:288  pass:254  dwarn:1   dfail:0   fail:0   skip:33  time:526s
fi-byt-n2820     total:288  pass:251  dwarn:0   dfail:0   fail:0   skip:37  time:517s
fi-elk-e7500     total:288  pass:230  dwarn:0   dfail:0   fail:0   skip:58  time:437s
fi-glk-2a        total:288  pass:260  dwarn:0   dfail:0   fail:0   skip:28  time:609s
fi-hsw-4770      total:288  pass:263  dwarn:0   dfail:0   fail:0   skip:25  time:452s
fi-hsw-4770r     total:288  pass:263  dwarn:0   dfail:0   fail:0   skip:25  time:427s
fi-ilk-650       total:288  pass:229  dwarn:0   dfail:0   fail:0   skip:59  time:422s
fi-ivb-3520m     total:288  pass:261  dwarn:0   dfail:0   fail:0   skip:27  time:502s
fi-ivb-3770      total:288  pass:261  dwarn:0   dfail:0   fail:0   skip:27  time:474s
fi-kbl-7500u     total:288  pass:264  dwarn:1   dfail:0   fail:0   skip:23  time:516s
fi-kbl-7560u     total:288  pass:269  dwarn:0   dfail:0   fail:0   skip:19  time:595s
fi-kbl-r         total:288  pass:261  dwarn:0   dfail:0   fail:0   skip:27  time:602s
fi-pnv-d510      total:288  pass:223  dwarn:1   dfail:0   fail:0   skip:64  time:522s
fi-skl-6260u     total:288  pass:269  dwarn:0   dfail:0   fail:0   skip:19  time:474s
fi-skl-6700k     total:288  pass:265  dwarn:0   dfail:0   fail:0   skip:23  time:539s
fi-skl-6770hq    total:288  pass:269  dwarn:0   dfail:0   fail:0   skip:19  time:488s
fi-skl-gvtdvm    total:288  pass:266  dwarn:0   dfail:0   fail:0   skip:22  time:444s
fi-skl-x1585l    total:288  pass:269  dwarn:0   dfail:0   fail:0   skip:19  time:503s
fi-snb-2520m     total:288  pass:251  dwarn:0   dfail:0   fail:0   skip:37  time:547s
fi-snb-2600      total:288  pass:249  dwarn:0   dfail:0   fail:1   skip:38  time:401s

8b962a9a16b3a4e3cc2a56cba82ee9c0dc0941b5 drm-tip: 2017y-09m-01d-13h-56m-06s UTC integration manifest
b14fe9611f8f dma-buf/fence: Sparse wants __rcu on the object itself
0ac977638e78 drm/syncobj: Mark up the fence as an RCU protected pointer

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_5565/
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Re: [PATCH 1/2] drm/syncobj: Mark up the fence as an RCU protected pointer

[Ville Syrjälä]

On Fri, Sep 01, 2017 at 03:57:06PM +0100, Chris Wilson wrote:
> We take advantage of that syncobj->fence is an RCU-protected pointer, and
> so sparse complains that it is lacking annotation.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  include/drm/drm_syncobj.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
> index c00fee539822..455660673259 100644
> --- a/include/drm/drm_syncobj.h
> +++ b/include/drm/drm_syncobj.h
> @@ -49,7 +49,7 @@ struct drm_syncobj {
>  	 * This field should not be used directly.  Use drm_syncobj_fence_get
>  	 * and drm_syncobj_replace_fence instead.
>  	 */
> -	struct dma_fence *fence;
> +	struct dma_fence __rcu *fence;

drm_syncobj.c uses that pointer directly quite a bit which seems to
generate more sparse warnings.

Would something like this be needed (just typing stuff blindly here)?

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 0422b8c2c2e7..1786787ecc30 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -106,7 +106,8 @@ static int drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
 	 * callback when a fence has already been set.
 	 */
 	if (syncobj->fence) {
-		*fence = dma_fence_get(syncobj->fence);
+		*fence = dma_fence_get(rcu_dereference_protected(syncobj->fence,
+								 lockdep_is_held(&syncobj->lock)));
 		ret = 1;
 	} else {
 		*fence = NULL;
@@ -168,8 +169,9 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
 
 	spin_lock(&syncobj->lock);
 
-	old_fence = syncobj->fence;
-	syncobj->fence = fence;
+	old_fence = rcu_dereference_protected(syncobj->fence,
+					      lockdep_is_held(&syncobj->lock));
+	rcu_assign_pointer(syncobj->fence, fence);
 
 	if (fence != old_fence) {
 		list_for_each_entry_safe(cur, tmp, &syncobj->cb_list, node) {
@@ -613,7 +615,8 @@ static void syncobj_wait_syncobj_func(struct drm_syncobj *syncobj,
 		container_of(cb, struct syncobj_wait_entry, syncobj_cb);
 
 	/* This happens inside the syncobj lock */
-	wait->fence = dma_fence_get(syncobj->fence);
+	wait->fence = dma_fence_get(rcu_dereference_protected(syncobj->fence,
+							      lockdep_is_held(&syncobj->lock)));
 	wake_up_process(wait->task);
 }
 
-- 
Ville Syrjälä
Intel OTC
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✓ Fi.CI.IGT: success for series starting with [1/2] drm/syncobj: Mark up the fence as an RCU protected pointer

[Patchwork]

== Series Details ==

Series: series starting with [1/2] drm/syncobj: Mark up the fence as an RCU protected pointer
URL   : https://patchwork.freedesktop.org/series/29700/
State : success

== Summary ==

Test perf:
        Subgroup polling:
                fail       -> PASS       (shard-hsw) fdo#102252

fdo#102252 https://bugs.freedesktop.org/show_bug.cgi?id=102252

shard-hsw        total:2263 pass:1233 dwarn:0   dfail:0   fail:14  skip:1015 time:9439s

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_5565/shards.html
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