2018-12-06 15:49:54

by Jerome Glisse

Subject: [PATCH] dma-buf: fix debugfs versus rcu and fence dumping v2

From: Jérôme Glisse <[email protected]>

The debugfs take reference on fence without dropping them. Also the
rcu section are not well balance. Fix all that ...

Changed since v1:
- moved fobj logic around to be rcu safe

Signed-off-by: Jérôme Glisse <[email protected]>
Cc: Christian König <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Sumit Semwal <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Stéphane Marchesin <[email protected]>
Cc: [email protected]
---
drivers/dma-buf/dma-buf.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 13884474d158..9688d99894d6 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -1048,27 +1048,38 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
while (true) {
seq = read_seqcount_begin(&robj->seq);
rcu_read_lock();
- fobj = rcu_dereference(robj->fence);
- shared_count = fobj ? fobj->shared_count : 0;
fence = rcu_dereference(robj->fence_excl);
+ fence = dma_fence_get_rcu(fence);
if (!read_seqcount_retry(&robj->seq, seq))
break;
rcu_read_unlock();
}
-
- if (fence)
+ if (fence) {
seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
fence->ops->get_driver_name(fence),
fence->ops->get_timeline_name(fence),
dma_fence_is_signaled(fence) ? "" : "un");
- for (i = 0; i < shared_count; i++) {
+ dma_fence_put(fence);
+ }
+
+ rcu_read_lock();
+ fobj = rcu_dereference(robj->fence);
+ shared_count = fobj ? fobj->shared_count : 0;
+ for (i = 0, fence = NULL; i < shared_count; i++) {
fence = rcu_dereference(fobj->shared[i]);
if (!dma_fence_get_rcu(fence))
continue;
+ rcu_read_unlock();
+
seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
fence->ops->get_driver_name(fence),
fence->ops->get_timeline_name(fence),
dma_fence_is_signaled(fence) ? "" : "un");
+ dma_fence_put(fence);
+
+ rcu_read_lock();
+ fobj = rcu_dereference(robj->fence);
+ shared_count = fobj ? fobj->shared_count : 0;
}
rcu_read_unlock();

--
2.17.2

2018-12-06 16:59:39

by Chris Wilson

Subject: Re: [PATCH] dma-buf: fix debugfs versus rcu and fence dumping v2

Quoting [email protected] (2018-12-06 15:47:04)
> From: Jérôme Glisse <[email protected]>
>
> The debugfs take reference on fence without dropping them. Also the
> rcu section are not well balance. Fix all that ...

Wouldn't the code be a lot simpler (and a consistent snapshot) if it used
reservation_object_get_fences_rcu()?
-Chris

2018-12-06 18:32:38

by Christian König

Subject: Re: [PATCH] dma-buf: fix debugfs versus rcu and fence dumping v2

Am 06.12.18 um 17:58 schrieb Chris Wilson:
> Quoting [email protected] (2018-12-06 15:47:04)
>> From: Jérôme Glisse <[email protected]>
>>
>> The debugfs take reference on fence without dropping them. Also the
>> rcu section are not well balance. Fix all that ...
> Wouldn't the code be a lot simpler (and a consistent snapshot) if it used
> reservation_object_get_fences_rcu()?

Yeah, thought about that as well.

Or even better move that code into reservation_object.c as
reservation_object_show_fences() or something like that.

Christian.

> -Chris