Re: [PATCH] dma-buf/sw_sync: Decrement refcount on error in sw_sync_ioctl_get_deadline()

[Dan Carpenter]

On Mon, Mar 31, 2025 at 02:02:44PM +0200, Christian König wrote:
> Am 31.03.25 um 11:45 schrieb Dan Carpenter:
> > Call dma_fence_put(fence) before returning an error on this error path.
> >
> > Fixes: 70e67aaec2f4 ("dma-buf/sw_sync: Add fence deadline support")
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > ---
> >  drivers/dma-buf/sw_sync.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
> > index f5905d67dedb..b7615c5c6cac 100644
> > --- a/drivers/dma-buf/sw_sync.c
> > +++ b/drivers/dma-buf/sw_sync.c
> > @@ -438,8 +438,10 @@ static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long a
> >  		return -EINVAL;
> >  
> >  	pt = dma_fence_to_sync_pt(fence);
> > -	if (!pt)
> > +	if (!pt) {
> > +		dma_fence_put(fence);
> >  		return -EINVAL;
> > +	}
> 
> Good catch.
> 
> I think it would be cleaner if we add an error label and then use "ret = -EINVAL; goto error;" here as well as a few lines below when ret is set to -ENOENT.
> 
> This way we can also avoid the ret = 0 in the declaration and let the compiler actually check the lifetime of the assignment.
> 

I had some issues with my email and it silently ate a bunch of outgoing
email without saving a single trace of anything I had sent.  I see
this was one that was eaten.

Unwind ladders don't work really well for things where you just take it
for a little while and then drop it a few lines later.  Such as here you
take reference and then drop it or you take a lock and then drop it.
Normally, you can add things to anywere in the unwind ladder but if you
add an unlock to the ladder than you to add a weird bunny hop if the goto
isn't holding the lock.  It ends up getting confusing.  With that kind of
thing, I prefer to do the unlock before the goto.

free_c:
	free(c);
	goto free_b;  <-- bunny hop;
unlock:
	unlock();
free_b:
	free(b);
free_a:
	free(a);

	return ret;

regards,
dan carpenter

diff --git a/drivers/dma-buf/sw_sync.c b/drivers/dma-buf/sw_sync.c
index f5905d67dedb..22a808995f10 100644
--- a/drivers/dma-buf/sw_sync.c
+++ b/drivers/dma-buf/sw_sync.c
@@ -438,15 +438,17 @@ static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long a
 		return -EINVAL;
 
 	pt = dma_fence_to_sync_pt(fence);
-	if (!pt)
-		return -EINVAL;
+	if (!pt) {
+		ret = -EINVAL;
+		goto put_fence;
+	}
 
 	spin_lock_irqsave(fence->lock, flags);
-	if (test_bit(SW_SYNC_HAS_DEADLINE_BIT, &fence->flags)) {
-		data.deadline_ns = ktime_to_ns(pt->deadline);
-	} else {
+	if (!test_bit(SW_SYNC_HAS_DEADLINE_BIT, &fence->flags)) {
 		ret = -ENOENT;
+		goto unlock;
 	}
+	data.deadline_ns = ktime_to_ns(pt->deadline);
 	spin_unlock_irqrestore(fence->lock, flags);
 
 	dma_fence_put(fence);
@@ -458,6 +460,13 @@ static int sw_sync_ioctl_get_deadline(struct sync_timeline *obj, unsigned long a
 		return -EFAULT;
 
 	return 0;
+
+unlock:
+	spin_unlock_irqrestore(fence->lock, flags);
+put_fence:
+	dma_fence_put(fence);
+
+	return ret;
 }
 
 static long sw_sync_ioctl(struct file *file, unsigned int cmd,